Best example ever amongst old time fans that saw him work of "We have no idea why he isn't in yet", but nobody can provide "compelling" evidence to convince enough people of it. It's weird. Everyone I've talked to that saw him wrestle or grew up with him on their TV in Chicago and Indy have stated he was one of the best. Nobody has ever effectively quantified why.
Homesteading (as much if not more than any HOF candidate I can think of outside of guys like Bock or Verne, and they don't really count) and playing second fiddle (by choice) to Dick the Bruiser are huge parts of why he isn't in, IMO. Lack of footage is a good chunk of it, too. Anything outside of a couple of 50's bouts that people see of Snyder now is when he was old, or at least looking old, in Chicago and Indy.
I hope he makes it in someday. It just feels like he should be there.