As for why it might be a point of contention with many millennials.
My best guess is we’ve spent years being accused of doing things by boomers who didn’t know that Gen Z was a thing and now it feels like we are being lumped in with Boomers because Gen Z can’t be bothered to learn that more than one generation camr before them.
For Gen X it may just be that they constantly feel forgotten and want to be known.