Demons and Terra Prime had nearly half of each episode devoted to Travis Mayweather. They just sucked, which is why no one remembers he was one of the main characters.
Demons and Terra Prime came 4 years too late for Mayweather. Basically, by that point, he was a guest character. It would have been like having the "nameless conn officer" on TNG have a 2 part episode devoted to them.
That's what Travis became as the series went on....the nameless conn officer. Except we knew his name.