i don't get it

I assume they are mostly manipulating the price up and down within a trading range and then riding it back as it reverts.
Not quite sure what they get out of putting on hundreds of 1 or 2 share trades though. They obviously have "special deals" with brokers/the exchange as brokerage would cost a mint for whatever information they get from it. Supposedly it flushes out large orders, but aren't they visible in market depth anyway? I don't get it and probably never will. I agree that there appears to be definite conflicts of interest with the supposed watchdogs.