As it simply a stylistic choice by Norman Lear since M*A*S*H, The Mary Tyler Moore Show, and The Bob Newhart Show, which were running concurrently, were shot on film? The Carol Burnett Show, which was also running on CBS around the same time, was also videotaped, but I don't that the lighting was that "harsh" as it was or may have been on AITF (https://youtu.be/gFMbx8-DhUE?si=f087bRWQ6HeTzuFN) or Maude.