Politics and the need to have the Core developers out. Some say it was because it would render Bitmain's Asic boost useless, and all other reasons that distracted us away from the truth. But I believe it was politics.
I will leave Achow and the rest more learned about the situation to comment.
What i have observed that Segwit blockage by Bitmain is one of the major reasons why some people are against segwit. Many myths are also created about this contradiction like Blockstream will have control over the bitcoin and they can dictate whatever they want but all these are just rumors nothing else.