Handing full access to the data on a user's device over to a company with the scruples of somebody like Facebook is a privacy nightmare, not "opening their platform a tiny bit".
Apple is not abiding, because they want to use time to really ensure they have the best assistant, before they allow competitors to build assistants for iPhone that can replace Siri (in the EU only probably)
It seems things start to get rolling in a way that they haven't since the start of the Google/Apple duopoly.
Apple's services revenue is showing a strong growth and it is entirely dependent on keeping the ecosystem closed so that it can take its commission and sell its services.
Once things get moving they would prefer still having control on the on the US market rather than making slightly more money(if any. No one wants this AI stuff as you can tell by the strong sales Apple keeps having despite or thanks to not having AI integrated) when the EU market is still open to them.