I'm familiar enough now about why the core people dislikes 2X. But, why was this accepted in the first place? Was it hidden as part of the original SegWit and the core developers did not know about it?
It wasn't really accepted. The backers of the proposal are just bored. They have money and they want Bitcoin core to die.
For years there have been differences between bitcoin "industry" and "users."
At least with this hostile takeover attempt, it's right out in the open.