The Bills only realistically had a chance to win the first SB. The other 3 were against better teams.
As for the first SB, I chalk it up mostly to the team, as was its wont back in the day, partying up until the wee hours of SB morning and being out of shape when game time rolled around. I also think that Marchibroda should have told Kelly that they're not playing the run and to keep feeding Thurman until they do.