Because they could spot and enter many small markets with "fish".

In finance and investment there is (to a first approximation) only one big market, and you are the "fish".

Those guys wouldn't have made their tuition walking into the Bellagio and entering the Big Game.

One of the guys actually did go pro and made a pretty good living at it for a while, besides writing some books and video series on texas hold 'em

http://www.businessinsider.com/how-andrew-seidman-started-pl...