There's an easy answer to this question. Lewis was terrified of prime tyson, wanted none of him. In the buildup to Tyson/Lewis, Lewis himself said he was thrilled when Tyson didn't make the Olympic team, and also said he wouldn't even have considered stepping into the ring with Tyson in his prime.

His personal life and later ring failures kind of tarnish his legend, but the fact remains that prime tyson is the most destructive force in the history of boxing. Period.