See T102581: the same basic thing applies to the dropdowns for page deletion: suppression-specific reasons are listed in the page deletion entry for the sake of oversighters, but are displayed for everyone. With that done, there's now a difference between how the revdelete and delete menus are handled.

There are separate pages for pages and files, though, so doing the same thing for page deletion would mean further balkanization by splitting off new pages for both MediaWiki:Deletereason-dropdown and MediaWiki:Filedelete-reason-dropdown (perhaps to MediaWiki:Deletereason-dropdown-suppress and MediaWiki:Filedelete-reason-dropdown-suppress, respectively).