Why do so many people think Joe Burrow will be great in the NFL?

I've seen too many times the next greatest qb of all time before he's taken his first NFL snap. Sam Bradford always comes to mind. He was touted as the next great one and never amounted to anything. For every 1 qb that has staying power and almost lives up to the hype there's 20 that don't. More often than not the QB's that do well aren't talked about all that much.