The bowl game loss probably wasn’t factored into the Heisman voting, but in two regular season losses, Detmer threw 9 interceptions. He was brutal in the bowl game loss, but votes were probably already cast.
In later seasons, there were a lot of similar system quarterbacks who didn’t get anywhere close to the same number of Heisman votes. The voters became more aware of these types of air raid system quarterbacks, and stopped voting for them based on their yardage and touchdown numbers.
These were quarterbacks at places like Hawaii, Texas Tech, Houston, etc.
When Detmer did it, the air raid was relatively new and people hadn’t seen those types of yards or numbers before. They gave him more credit at the time. It is looked at differently now. No one could ever win the Heisman these days with two losses with nine interceptions. That would be a total death blow.