The available tv time world wide is huge. The market demands new ads frequently, the size of the marketplace for consumer goods is skyrocketing. The pay goes up, the job is more attractive. Lawrence Olivier was once asked why he accepted jobs on TV, since that was considered a step down from movies and theater. His answer, “It pays well, and it’s so damned easy.”
That bit isn’t on any of Newhart’s CDs. That’s not to say he didn’t do it, of course. If he did, it was prompted by Olivier’s ads for Polaroid cameras, which were shown only in the USA.
Didn’t Cher say that her acting career was derailed by doing an infomercial which ran and ran and ran? Lori Davis hair products or some such thing.
Laurence Oliver may have gotten away with it because there were a number of articles in the 1970s saying he was opening appearing in horrible films like “The Betsy” in order to leave a large enough estate for his family when he died. Plus people thought a Shakespeare male actor could get away what a woman with a cheesy pop music/Vegas/uncool non drug user couldn’t.