Because everyone is on a spectrum. [xyz] wasn't the straw to break this user's back, but it will be the tipping point for some number of users. [xyz] is also moving this user closer to the edge, so when Apple does [abc] the sum of both is now enough to move this user.

You can't expect that everyone who is bothered by an issue switch away from a platform. The switching cost is significant (and Apple works hard to make it as high as possible). Not to mention that the platforms (really one notable competitor) that they are considering switching to also have [def] and [ghi] that the user doesn't like which is also counterbalancing the decision.