I never had any frustration about writing uncredited. I always felt that the satisfaction of doing it was in the doing of it, really, and getting recognised by the small number of people that know what you did.
I write scenes - often quite long scenes - mainly because I still get seduced into writing six lines where one and a half will do.
A writer ought to be the best possible source about their work but the writing instinct doesn't come out of self-examination. That part of yourself in your work is expressed willy-nilly, without your cooperation, motivation or collusion. You can't help being what you write and writing what you are.