Why was Leon Spinks such an oustanding amateur but underachieved as a professional?

Okay he conquered Muhammad Ali albeit a 36 year old Ali but after that he never really crusaded towards greatness the way you would think that he hould have. As he had such an oustanding amatuer career ie won the inaugural 1974 World Amateur Championships and then won the 1976 Montreal Olympics while beating the favourite from Cuba in the final. His brother Michael was had better succes as a pro as he was an undisputed light - heavyweight world cahmpion and then moved up to heavyweight and handed Larry Holmes his first loss as a professional albeit a 35 year old Holmes but Larry was still a pretty good fighter at that time as he beat Bonecrusher Smith, Tim Witherspoon and then went on to beat Ray Mercer a few years later. And Michael also has a good victory over the dangerous Gerry Cooney as he knocked out Gerry in 5 rounds in 1988. So it is a littlebit surprising that Leon never accomplished more as a pro as fighter with amazing amateur careers normally make great pros ie Muhammad Ali/Cassius Clay, Ray Leonard, Pernell Whitaker, Amir Khan, Roy Jones (should have won Olympic gold), George Foreman, Joe Frazier, Mike Tyson (Tyson surprisingly had a great amateur career), Michael Dokes, Lennox Lewis, Ray Robinson (never lost a fight as an amateur and was too young to enter the 1936 Olympics in Berlin), Riddick Bowe etc. Although it is hard to critcise Leon as he was a World Amateur Champion and an Olympic Champion and then battled and beat Ali after 6 or ten fights or something lol. Seven fights I think it was before he fought Ali. In my opinion Leon would have made a better cruiserweight as he would have been too light to fight the best heavyweights during his era as he got demolished by Homes and Coetzee after he beat Ali. And Ali's power would have not been the same as it was in the 1960s and early 1970s when he fought Leon whichwould have allowed Leon to go the distance twice with Ali. If a younger Ali had fought Leon then he ould have beaten Leon inside the distance a did Holmes and Coetzee. But ifthe cruiserweight division would have existed when Leon turnd pro then he would have probably been unbeatable in that weight class. Instead Leon had to move up from ight - heavyweight and foughtat heavyweight weighing about 203 lbs against men who weigt 220 lbs or more ie Holmes and Coetzee. And Foreman would have also annihilated Leon if they fought during the 1970s. Maybe Leon could have scraped decision victories against Frazier and Norton but even that is unlikely as they hit pretty hard as well. But all due respect to Leon nevertheless for achieving what he did although it could have been even better.