I agree, I don't get booing your own players too
It seems to be one of those things that people have picked up on after hearing it on tv and/or social media
Imho real fans would not boo their own players during a game, and personally I would not boo at the end either, though I can understand why some people like to demonstrate their feelings in that way
I'm in my early 50's, maybe it's a generation thing?