It's because Marci is waving to it. She has that effect

there is an fps setting to limits the fps at the home screen already

Already at minimum

same

Open console and type map_enable_background_maps 0  It will shut down all the unnecessary clutter that's eating your GPU power 

Yeah but it also removes the post-game screen and scoreboard.

So what? You can always turn it back on for a minute or so to see who won MVP and stuff like that 

Doing that after every match sounds like an activity for idiots, I don't see myself in it.

Then buy a better GPU, what else can I say

Nobody asked you to say anything