As you point out, Wells co-wrote the screenplay for "Citizen Kane", with Herman Mankiewicz. Aren't screenplays a form of "literature"?
Some screenplays are adapted from novels or plays, some are not. But if the "written" version of stage plays are a form of literature, why wouldn't screenplays qualify as well?
Movie scores are a form of music, aren't they?
I'll grant that few people read screenplays. But few people read some other literary works, too.