How about cultural reasons instead of political ones ?
An Invention originating in China:
The world's first known movable type system for printing was made of ceramic materials and created in China around A.D 1040 by Bi Sheng (990–1051) during the Northern Song Dynasty (960–1127). When this technology spread to Korea during the Goryeo Dynasty in 1234, they made the metal movable-type system for printing. This led to the printing of the Jikjisim Sutra in 1377, the oldest extant movable metal print book. The diffusion of both movable-type systems was, however, limited.
This only makes it more likely that China or Korea would have first developed the systems further, as Japan generally adopted them decades or centuries later.
Also see below.
The reason it was not used to its full extend:
They were expensive, and required an enormous amount of labour involved in manipulating the thousands of ceramic tablets, or in the case of Korea, metal tablets, required for scripts based on the Chinese writing system, which have thousands of characters.
This was the biggest reason, but Hangul, a featural alphabet, had been invented by Sejong in 1443, which didn't exactly cause texts to be printed in the newer writing system.
The uniquely Japanese solution and also a potential POD:
Kana (仮名) are syllabic Japanese scripts, a part of the Japanese writing system contrasted with the logographic Chinese characters known in Japan as kanji (漢字).
This would essentially have been impossible for two major reasons.
The literati in both Japan and Korea solely used Chinese characters for official documents, despite the fact that rural people (primarily farmers and laborers) continued to use Kana and Hangul in local texts (primarily folk tales) for centuries. The latter systems never became widespread until the 20th century or so because aristocrats were extremely wary of abandoning a complex writing system that had been culturally ingrained, as adopting egalitarian systems would blur the distinction between the upper and lower classes.
Additionally, the Chinese characters themselves had become such a part of the Korean and Japanese language to the point that even native
words were represented with the characters themselves. While this often made it difficult to tell whether a word should be pronounced in the native or Sino-Japanese/Korean versions, the general concept
of the idea expressed within each character remained the same, albeit with different nuances. As a result, the complex relationship among these systems would have been broken had each "word/syllable" been written according to pronunciation, making the syllabary/alphabet even less receptive to the literati. Pronunciation was even worse for Japanese because its restrictive phonology led to a large amount of homonyms, which had been easily resolved with the nature of Chinese characters (closely mapped to meaning), not to mention the multiple pronunciations from Go'on, Kan'on, and Tō'on (On'yomi/Sino-Japanese) and Kun'yomi (Native Japanese) frequently mapped onto each
Meanwhile, Korean also had a similar system for centuries, as each character was pronounced according to the Sino-Korean or
native forms (although there was generally only one Sino-Korean pronunciation for each character) through the Idu, Hyangchal, and Gugyeol systems until the late Joseon period. However, only the Sino-Korean readings remained by the 19th-20th centuries, possibly due to Hangul's influence, while homonyms were less of an issue (due to a larger phonemic inventory), which meant that although a mixed-script continued to be used throughout the 20th century, Chinese characters were phased out by the 1980s-90s (although it is still used in highly specialized cases).
In any case, Japanese still uses a mixture of Kanji and Kana for the reasons stated above.
Solely quoting a few minimal passages from Wikipedia doesn't provide the whole picture, as you can see above.
Oh I see that's much easier to explain, as Japan was in fond of Chinese culture the whole time she might be pleasant to learn from her. But I think we can explore the possibilities for the political reasons: the Shogunate eager to achieve tech advancement for competition with other nations?(like China?) The Chinese war with Japanese and subdued the country to be a vassal, which brought the techs due to open borders?
A war between China and Japan would require one of them either conquering or allying with Korea due to logistic reasons, as well as a ruler willing to entirely ignore the complex system of tributary relations that had existed for decades beforehand. Focusing on the 13th century and after, this occurred twice when the Mongols (nominally ruling a Chinese dynasty) attempted to use Korean and Chinese ships to invade Japan, and during the Imjin War when Hideyoshi invaded Korea in order to eventually "conquer" East, South, and Southeast Asia. However, had the wars been expanded, either could have severely devastated Japan (the latter involving a counter-invasion by China after a direct Japanese invasion), which would have severely delayed developments for at least several centuries after widespread destruction of arable land, forcing it to rely even more on China.
For a relative comparison, Korea was more developed than Japan on multiple levels (including a larger population) until the 13th century, but was devastated during the Mongol, Japanese, and Jurchen/Manchu invasions, each involving several million casualties, along with countless wokou raids (800+) along the Korean coastline from the 13th to 16th centuries, further limiting population growth. As a result, the population did not managed fully recover until the late 17th century, with an influx of cash crops post-16th century, as the population suddenly increased from around 6-8 million in the early 17th century to around 10-15 million by the 19th century or so (10-12 million by the 13th century).
Had the Imjin War been butterflied away (with a more diplomatic shogun), both China and Korea would have been much more focused on the northern frontier, potentially enabling them to gradually expand into Western and Eastern Manchuria, respectively, somewhat boosting population levels over the long run. However, this wouldn't have significantly affected society and technological innovations over the long run, as there would have been even less pressure to develop military technologies after the 17th century.
Not at all. See above.
By the late 15th century, various pressures had forced a handful of European countries to expand their trade routes to the east, south, and west, which fed into a collective cycle of innovations to make up for limited resources and a relatively small labor force. However, the Chinese market alone had dwarfed the collective European market for over a millennia, which meant that various entities across Central, East, and Southeast Asia collectively paid tribute in order to gain access to the large market. As a result, there were no significant pressures for China (as well as Japan and Korea) to continuously pursue technological innovations for centuries that would have collectively led to industrialization.