In case anyone doubts my premise: in film, directors are usually the ones with ultimate creative control behind the project and are the ones whose names are most prominently billed. (i.e. “A John Smith Film”). But in scripted TV, creators and showrunners are typically writers or former writers, and directors are comparative unknowns (unless they’re writers that crossed over into directing).
By job description, a director has more ‘small details’ to take care of per minute of result. For a single feature, the director can take care of all of these little details himself, or delegate some of them to an AD or other staff and still be confident that they’re being done right. Because the director’s influence has so much effect on the overall film, not just the plot and the dialog, he has more creative effect on the feature than the scriptwriter, leading to Auteur Theory
In a television series, though, there’s more to shoot and less time to do it in. No one director can be responsible for an entire season of television the same way that he can for a feature film - there may be several important directors working in rotation. This still makes them a strong influence over the show.
However, the writers, by the nature of their work, can delegate better over the long-term, with a showrunner sketching out a season’s plotlines in general, and giving the series writers their marching orders for individual episodes.
That’s right. A director on TV has little opportunity for creative input. His job is to get the scenes shot and not fall behind schedule or over budget. He may not even get the script until a few days before shooting. The actors are usually set in their roles, so he can only do a little toward telling them how to interpret them.
In addition, the “look” of the show is usually set in advance, so he can’t change that.
Arguably PRODUCERS are more prominent for television. You can probably name FAR more TV producers than TV writers. It’s just that in TV the producers are either writers themselves or in on the creative process.
Note that there are exceptions. Green Acres is much more director Richard L. Bare (who did the same type of gags in his Joe MacDoakes comedy shorts) than producer Paul Henning (whose Beverly Hillbillies and Petticoat Junction were far less absurd).
But Bare directed all the episodes, so he was able to take more control.