The de-listing of Coinbase’s bitcoin wallet platform followed a major upheaval in the Bitcoin community, as many of its members began to contest against Bitcoin.org’s unsupported decision to remove the world’s 2nd largest bitcoin wallet application from its website.
http://www.newsbtc.com/2016/01/10/bitcoin-org-violates-its-mission-statement-to-censor-coinbase/
I think their argument would be that Bitcoin XT is a fork and therefore and alt-coin and therefore not bitcoin and therefore they are no longer supporting bitcoin.
Right or wrong, I believe that is what they would say at least in part.
If XT is supported by 75% of the payment processors and miners, then Core is the fork. The community decides.
XT is dead. But Classic is still alive. I think it is better for the Core team to declare that it will increase the block size soon.
XT itself is dead. Done for. The new "Classic" proposal will fare no better, see the comments above on what this so-called democracy will do for banks. Supporters of a fork will play right into government hands.