In theory we can get all in and all out in seconds, and we all can only profit from the pool of money which is lost, the big guys risk billions to secure a few % of this pool, so there never going to be able to make more than 10% area.
Where an individual trader could run a 10k account upto 100k, 900% gain, and the gain is so small the market wouldnt really notice it.
Ofcourse if loads where to do above, it would badly affect the banks profits, but its rare only 0.01% of us, ever get to that kinda level, if not less.