Jagex's main profit is from cheaters.
Why?
Players who cheat usually have a membership account either from the money they make botting or from the rsgp they sell. These kind of players won't leave Runescape as they gain profit from it and enjoy the cheating. On the other hand, players who don't cheap aren't found online as a bot and the chance a real player will buy membership depends on how busy he is in real life. Basically, cheaters will buy membership no matter what and legit players won't.
Jagex has to ban a portion of the players who bot so they have regular players as well - players which will hold up the Runescape community. After all, if there weren't any real players, there wouldn't be much a reason to continue developing the game and to expand the company.
BTW, go to the miner's guild in EVERY world (including members). You'll see a swarm of at least 30 botters.