I would think that forging even an average players signature has to be beneficial in the long term for the person talented enough to pass them off. A few bucks here and a few bucks there can really add up when selling in volume. The average person would not take the risk but these people are pros and think nothing of it.
Then there are the ones that seek out a skilled hand to produce some of the rarer autos in the industry. When you do a search for "what are the rarest sports autographs" < those would make a nice starting point for this type of person then they'd add in the HOF'er autos and players that have died as well = big money. This happens a lot more than most of us would like to admit... and when it does it is prudent to report it in the hobby...
Then there are the kings of forgeries that go in to all aspects of the sports collecting industry (e.g. autos, uniforms, etc.). This article talks about one of the kings of the hobby that is making big rocks in to little rocks because... well... he BROKE THE LAW a lot.
https://deadspin.com/5818225/the-dow...-bernie-madoff