I thought it was because he wasn't included in the first full class (not counting Andre going in solo to start the Hall, I don't think he has beef with that.)
He's kinda resentful that they want to make money off of his legacy.
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Thank you, Eddie Guerrero.
http://www.wwe.com/f/styles/photo_large/public/photo/image/2012/04/33_Moscow_04112012jg_02128.jpg