Although producers argued this was a spin off from the movie and not the subsequent TV Series, who's kidding who? It was meant to cash in on the popularity of the TV series which was super popular in 1979.
So Wayne Rogers is going to age to look a great deal like Adam Cartwright I guess. Trapper was a serious medical show in the hollywood fashion, with Gregory Harrison in tow(fresh from Logan's Run) as the young good looking Viet Nam vet Doctor "Gonzo" Gates.
The series ran from 1979-1986 when it started to look dated next to shows like "St. Elsewhere". You occasional heard mention of Hawkeye and the 4077 but nobody ever stopped by sadly...
Just wanted to add: Wee67 pointed out that the above video has scenes from the pilot. Look at Trapper's office adorned with pictures from M*A*S*H, has nothing else happened to the guy in the past 27 years?