It isn't always money. Sometimes it's just lulz.

Reply All had did a podcast (ep #178) about people who are running bots on Counter-Strike that ruin the game. They tracked down a person who does this and they just basically do it to be annoying.

> [... ]what’s the point of running them? Like, what do you get out of the exercise?

> There are many reasons to run them. Most if not [all] casual players dislike bots (which is a reason to run them)