Why did he never have a big job, then? I guess it is possible he never wanted one, but I kind of doubt that because he was going to come to Knoxville until they pulled the plug on Currie. I think university admins were scared (and perhaps wrongly) by the offense he ran and the fact that he never was a 100-hour-a-week recruiting warrior. His personality, while endearing to fans (at least when he was winning), I could see as being off-putting to well-heeled boosters or if the team started struggling. If he coached us, can you imagine if after a tough loss to Kentucky he showed up at a press conference talking about pirates or what his favorite Halloween candy was?
Leach was a good coach, but taking bad programs and making them decent or pretty good isn't HOF material. The HOF is the HOF...it should be reserved for the greatest coaches of all time, and I don't think Leach is one despite unquestionably having an impact on how offensive football is played and generally being hilarious.