The hall of fame is a bit silly, and it's a bit silly to worry about who gets into it (though I used to myself). Reasons for a fighter not being included can include: how famous they were; how famous they are; friends in the industry now; are they alive?; if they are dead how has their image been reclaimed since their death (big book for example); what is their nationality?; have they played ball with the Hof owners; is their inclusion likely to bring the HoF owners money? I've been involved peripherally in HoF induction and it's ludicrous. Often the people voting do not know the names of the pioneers on the ballot form. I had one writer outright ask me why he had never heard of a certain fighter. The obvious answer, "because you are an underqualified idiot" was not politic.
Probably because he only made one successful defense in three championship reigns. Granted two of those defense losses were to Matthew Saad Muhammad and Eddie Mustafa Muhammad.
It is disappointing that Marvin is not in the IBHOF. He was a great fighter that was better than many of the Light Heavyweight Champions over the last 40 years. Ironically, I met him at the IBHOF weekend a few years ago. Great guy. I ended up driving Marvin and his cousin to the IBHOF cocktail party. He discussed the current state of the light Heavyweight division and felt he would beat them all. When I mentioned guys like Michael Moorer at LHW, he and his cousin laughed and said Marvin would knock Moorer out.