i've wondered the same thing too. It seems that the republicans were equally as guilty. Marvin Leath and Kent Hance were both unopposed in 1980 and could maybe have been defeated.
Freepcrusher, this topic was kind of targetted at you.
Hance holding TX-19 in 1978(over W. of all people) as a non-incumbent was quite impressive. That seat went for Ford 58%-42% in 1976 and was voting over 60% Republican for governor and Senator in those close races that year. I guess Bush was(and still is) that bad.
Leath's district was actually still fairly Democratic. I believe it went for Carter in 1976 and as late as 1990 was voting for Ann Richards for governor.
It seems like for the most part nationwide, it was Republicans who missed all of the golden opportunities to pick up House seats in the 1970's and 1980's.. FL-11, GA-07, VA-05, NJ-03, too many to mention really.
This was really the only one why I dont get why Democrats didnt contest strongly every year. Bill Green in NY-14 was the other. And its not even like Fields had a moderate or liberal voting record like Green did. He was a Gingrich-like conservative.