Well, time for another post full of probably incorrect assumptions, but a shorter one. I've always meant to mention this, but to my surprise I can't find an animation-related post where I brought this up: I've always wondered why Tedd Pierce and Michael Maltese, two Warner Brothers cartoon writers who also did voice acting, more or less stopped acting after about 1951. They continued to write cartoons for the studio, but Pierce's last known voice job at the studio -- maybe there's a later one I didn't notice and didn't make it onto IMDB -- was in 1951, and so was Maltese's. It's particularly surprising in the case of Pierce because he was a really good, versatile voice actor who performed in other people's cartoons (like the Babbit and Catsello cartoons), not just his own.
Thinking about this, I recalled that Tex Avery was another cartoonist/performer who didn't do much voice work after about 1950. So it may have been an actual trend at the time, toward a more professional approach to the art of voice acting. Thanks to Mel Blanc and others, voice acting had already become much more of a profession than it had been in the early days of sound cartoons, when voices were as likely to be performed by an animator or writer as by a full-time actor. In the late '40s into the '50s, it seems like the studios shifted even more strongly toward hiring professional actors for everything. So if there was a small male part at Warner Brothers that Mel Blanc wasn't doing, it might have gone to Pierce or Maltese in the '40s -- but in the '50s, it would have gone to Stan Freberg or, later, Daws Butler. Just as in Avery cartoons, the parts he once did himself probably went to Butler or Don Messick in the '50s.
This isn't a trend that lasted, since the non-professional voice actor actually came back -- mostly in TV animation. (Bill Scott didn't get to do much voice work at Warners or UPA, though he did get to do the funny-animal voices in the UPA cartoon sequence in the movie The Girl Next Door. But in television, he became as prolific an actor as he was a writer.) I just wanted to make a note that there does appear to have been an "actors act, writers write" idea in the later years of theatrical short cartoons.
Here's my favorite Mike Maltese voice job, in 1948's "A Feather in His Hare" (though the first sounds the character utters are not from Maltese but Mel Blanc, who was called upon to do the screaming).