The simple answer is, "There is none."
For some reason, year after year, I continue to read things from fans about how so and so "isn't deserving." My question always is, "How can they not be deserving if there is literally no criteria?"
Please stop trying to apply your own criteria to the WWE Hall of Fame. In addition to that, please stop asking why so and so isn't in yet because there's clearly a template to each HOF class, and you can't put everyone in all at once.
Could Rick Rude have gone in before now? Sure. Should it bother you that he is just now going in? Absolutely not.
You shouldn't even look at this thing like a Hall of Fame (despite the name) because it really is much more like a Kennedy Center Honors deal. It's a way to add a little sizzle to WrestleMania weekend, and it's a way to honor folks who contributed to the business.
It also appears to be something that can be used to get marketing deals, etc. done. For those who get inducted, it's a nice additional way to market themselves at conventions, etc.
Why am I sick and tired of hearing people get all in their feelings about it? I look at this way. In an industry that has a long and proud tradition of chewing up talent and spitting it out, I am glad those folks get a night to be in front of an appreciative crowd once again.
The other prong of this is you see things about, "How WWE does this type of thing for the wrong reasons." To that I say...grow up. These people who are accepting the inductions know what the deal is. I don't give a crap about what ulterior motives the company has. I enjoy the event, and if you don't like the lack of criteria or whatever then ignore it.
Getting up in arms every single year about the inductees, lack of criteria, etc. is a fool's errand in my opinion.
Appreciate this deal for what it is....or don't. Either way, stop trying to apply your own criteria to a Hall of Fame which does not have a stated one. That is a tremendous waste of time and energy.