Unless they have house players getting all the good hands (which would be really brazen and obvious), greed should lead them to run a straight-up game, not a rigged game. They might make more rake from a rigged game, by a pretty marginal amount, in the short run. This is true. But in the long run they'd hurt themselves way more than they'd help themselves.No incentive for a site to cheat? Because I know you personally and I know your character, I can honestly say that I believe that you honestly believe that. I personally would like to believe that, based on your example of sites “blissfully raking in pots,” I can understand the thought of why would they need to cheat.
One word my friend, “ GREED!” What is plenty for some is never enough for others.
It would be fairly easy to do an informal statistical analysis that shows, for example, that draws come in far more often than they should, or AA/KK and other cooler matchups are much too frequent. Someone on this site already attempted this for Poker Mavens (and came up empty), and if there were real suspicions, I'd expect folks on 2+2 to go at it pretty aggressively. People out there do care about this stuff and know how to analyze it.
As soon as someone demonstrates that something's off about a site, players will start disappearing. Even if it's a small number of players, it won't take much to offset that marginal increase in rake caused by more "action hands." In reality, it would probably be a very large number of players, since no one wants to play at a site that can't be trusted.
Not saying it couldn't happen, but it would be very surprising to see someone who invested the time and resources to build a poker site and player base piss it away on such a slim opportunity for short-term profit. Someone that stupid is unlikely to have gotten the site up and running in the first place.