Not only because of poor pc, but loosing interest in game.
You really can't have fun because of bots, muted f2ps, crappy default settings, lack of updates ( that includes class and weapon rebalancing, new weapons [plz], new mvm missions, etc.), the majority of community that are coo coo crazy and a lot and a lot of problems in tf2.
I know it's sad that Valve drop tf2, but sooner or later it will obviously happpen, nothing lives forever.
Tf2 will stay in my heart, if didn't spend a lot of hours, I wouldn't be here.
So long, mercenaries!