[bityard]

Could the origin of Exposure Bucks?

Someone can correct me if I'm wrong, but I believe these days the various film-industry unions essentially require individual credits for anybody who even tangentially had anything to do with working on the film or on the set of a film. E.g., I'm pretty sure I've seen the names of catering staff in movie credits.

[schlauerfox]

It's all contracts. My father is named because the effects company he worked for had a contract for credit, the guilds similarly enforce their contracts on producers. It was common for many many people involved in production directly to not get credit, you may be underestimating the sheer number of people involved in making a major film. Industry people joke that the caterers are very important, and to be listed above them is a privilege, but a wry hint of truth because an army moves on its stomach.