Joining the servers as players is one way to do it.You misunderstood, the “bots” aren’t hosted by the server owners. They’re accounts that join a game as players.
They act as aimbots and are able to run around the map on their own.
They’re made with the express purpose to ruin the game.
Ruining the game on purpose is another thing. Are we sure they're using aimbots? I mean, they're bots, so it's obvious, but I mean in the classical sense "one shot = headshot"? And is every bot there for that purpose? The last time I played TF, which was a while ago, the bots I described were quite common and bots that ruin the game on purpose were few. More people that ruined the games on their own by using aimbots or other tactics that ruined the game.