Like fubar said, we can't really automate anything else easily. In this post anyx discusses the costs of running cheetah, I recall him saying that trying to create something to find plagiarized photos would astronomically expensive.
People complain about bots enough as it is. Steemcleaners is not a bot, every post, every comment that the steemcleaners account makes is made by a person. Every post is investigated, commented on, reviewed, and logged by a person and that takes a lot of time and effort. The money made is going right back to all the members of the community(steemcleaners or not) who identify and report abuse. Most of us even use our personal accounts voting power to deal with these issues as well, despite the risk of retaliation. Hell, look at my account, I'm no whale. I use my meager voting power to take care of small issues to save steemcleaners voting power for the really big ones.