Let's go clubbing!
They don't. Well, most don't. It's attention whoring. The people doing this get a big ego boost when they see the bots being such a major topic of conversation, almost to the exclusion of the rest of the game.Why do these people hate a free to play hat trading game this much
And this.Originally it was out of spite for valve actually fighting lmaobox - that was when multibox started existing.
Currently different people do this for different reasons - spite for valve/tf2, monetary gain and/or simply for shits and giggles. It's nothing more than "pissing on someone's grave" to them.