The issue is that the list is infinite (anything not specified is UB), so actually removing any finite amount of UB from the list won't make it shorter.
(only slightly tongue-in-cheek, I do believe that removing silly things is worthwhile).
To be undefined behaviour, it must at least be valid syntax. The syntax is described in a finite document. Also it only gets executed by a finite machine, that has a finite number of finite descriptive documents.
