It turns out that screen credits are largely determined by the union contracts. Over the years, in difficult negotiations, the AFM (American Federation of Musicians) has traded screen credits for better pay and working conditions.
This seems reasonable, until you realize that somehow other unions have won concessions without giving up credits.
Ultimately, of course, it shouldn’t be a matter of union contracts. It’s a matter of fairness.
As Spike Lee might say, do the right thing.