Then why did the worst event in Irish history happy in the 1840s? Keep in mind that the UK was punishment for Ireland's freedom struggle in 1798.
Because the potato blight doesn’t give a damn if Ireland is part of the UK or not. It would have struck the Irish just as hard, if it had hit Ireland half a century earlier, and the British, in general, would likely have cared just as little. Heck, they might even have cared less, if it had happened earlier, since it could have happened during the American or French revolution where Britain would have been more busy elsewhere. Saying that the Irish catastrophes in the 1840s are dependent on the Act of Union is very much a reach. Furthermore, to your original question, Ireland and Britain have a much longer history together (even if much of it might be shitty) and are geographically located next to another. It made sense to unite these realms. It might also have made government more streamlined and smooth, which I would imagine is what they really cared about. Hanover, on the other hand, is something most of the British elite didn’t care for and most people’s reaction when Vicky took over and they lost it was “good riddance” and in Hanover, the feeling was mostly the same. Why should anyone want to unite these realms?
The Royal family at the time was mostly German by ethnicity with essentially no Irish blood
It’s always the blood stuff with you, isn’t it? Firstly, I don’t think that many gave a damn that the royal house is/was mostly of German descent. Most people just accepted that they were the kings and the people who didn’t mostly cared because of religious reasons. Bonnie Prince Charlie was not a bit more of English blood than the Hanoverian kings you so seemingly despise. Hell, outside Germany, very few royal houses were actually “of national ethnicity” and guess what? It doesn’t matter. It still doesn’t, since they, through their role and upbringing, represent it in a different way. And honestly this whole blood nationality thing is veering uncomfortably close to the one-drop myth and other racial theories
In short:
Yes, Hanover isn't contiguous with Britain, but neither is Ireland.
It might not be contiguous by land, but by sea it’s literally right there so geographically it makes sense. Also, for good or bad (mostly bad) Ireland and England have a shared history of millenia unlike what England had with Hanover.
What would have happened if the British had left us alone and used Hanover to fulfill their dreams of a United Kingdom instead?
And finally, as shitty as it is, they didn’t give much of a damn about what the Irish thought. That doesn’t make it right, but it makes it history. It’s not about what makes it just in our modern eyes, but what was logical for the people in charge of the time.
I have seen you make a lot of posts like these lately, where you have made your views on the Hannoverians, the Stuarts and English rule over Ireland and Scotland very clear. While I don’t disagree that much of what the English did was shitty, and while I personally also prefer the Stuarts to the Hanoverians, you cannot simply analyze history with our present views of rights and justice. Those were not the prevalent views of the time and it is very narrowminded to think that much could be done better/differently simply because we think they should. Because, sadly, most people in charge simply did not care