It's a combination of the two factors. If a group of people want to one up each other by refactoring their side projects to be as woke as possible, that's fine by me. But if they're doing it and causing breakages and/or forcing everyone else to adapt, that's where I draw the line.

>A vendor changing something like this is par for the course, right? Why such an extreme reaction?

I'd be similarly pissed off if an upstream API provider suddenly decided to change all their identifier names for stylistic purposes. eg. the CTO woke up one day and decided that all of their API endpoints should be changed from camel case to snake case.