The problem is that it creates a problematic incentive structure.
I haven't seen them publish any hard statistics, so how can a group know if it's just them that got rejected for funding, or if it's pretty much everyone who applies?
Investors, on the other hand, play the game more regularly. It's impossible to keep the information from them long term. If they had to pay to come, they would need to be finding good investments. Startups don't have this feedback, at least not without things like public complaints.