Right, but that stereotype is largely driven by real life data points suggesting that they DO, in fact, need agents, guidance, etc. If there's such a large disparity in the league among players going broke after retirement, I think that's as strong an indication as anything of not being financially savvy enough to think they can navigate that alone.
But mostly, from the NFL's perspective, they just don't want to deal with players directly, because they're super fucking stubborn, oftentimes emotional, and work at a pace that doesn't benefit anybody but themselves.
Exact same reason if you ever went to buy a house, you'd rather deal with a buyers agent than the actual buyer. Actual buyer is going to be significantly more difficult to get through to.