In case you missed the memo, the way Bitcoin works now is the code changes are decided by the big players like Coinbase.
No. Code changes are decided by the majority of Bitcoin Nodes. If one side decides to go to one code and the other don't, they will fork. Coinbase can't do anything except manipulating prices.
Their opinion carries weight in the West at least. They'll also be in touch with the other big players in the infrastructure and perhaps form a united front when the time comes.
No one wants to be caught out on the wrong side of the decision.