Fielding candidates in unfavorable districts might seem like a waste of precious resources to a party—and most of the time, it is—but it's also a responsibility.
Having a decent number of staffers available gives state legislators a better ability to make competent, independent decisions and to resist the influence of other actors.
Is there something to the idea that a politician who no longer faces re-election is free to pursue new policy solutions without needing to kowtow to special interests?