EditRightsConstraints does the check $this->performer->isAllowed( 'edit' ) which checks if the user has the ability to edit pages in general and not just this specific one. I think this check is too restrictive. It means that if someone writes an extension hooking into userCan to give edit rights for a specific page but not all pages, this won't work. I don't see any benefit to making the check this restrictive.
Looking in git blame, it seems like the check in question was originally added by RobLa in 2005 when the notion of "edit" rights was first created (a2a28a34c1fc / T2996). Presumably that was before we had per-page rights like we do now.
I propose adding the title to the check.