It’s pretty hard, because Madagascar is one of the last settled places on the planet. Omani influence in east Africa is pretty high because there’s been a long history between Iran/Persia, the Arabian Peninsula, and East Africa, with trade ties possibly going back further than 1000 BC. There was regular trade between the Arabian peninsula and the East African coastal city states during the Ancient Greek and Roman periods, whereas Madagascar was still composed of subsistence hunters. There’s just not a lot of reasons to go there.