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?
2X was never accepted by Core and was not sneaked into the codebase either.
It simply is a fork of the original Bitcoin code, maintained by a different development team, backed by various members of the industry and parts of the community. It came to life due to some people persisting on (1) on-chain scaling as being the preferred solution on the one hand and (2) adding a short-term scalability fix on top of SegWit on the other.
So are 2Mb blocks here then? I think larger blocks are extremely destructive to Bitcoin's future. In fact I believe that the blocksize should be halved, and generation frequency increased. I believe that it will have to happen in the future, so why not do it now.
SegWit blocks can theoretically reach close to 4MB:
https://medium.com/@jimmysong/understanding-segwit-block-size-fd901b87c9d4