That doesn't totally surprise me, I have heard Lucille Ball was a perfectionist and didn't allow bloopers on her show despite how zany it was. Now Andy Griffith and Frances Bavier I have heard are a lot meaner than their on screen roles (until Andy's personality changed in the color era), but that must have been away from the set.

https://www.decades.com/articles/heres-why-little-ricky-said-the-set-of-the-andy-griffith-show-was-more-fun-than-i-love-lucy?fbclid=IwAR294c8_RHln6HFy1XR58B09O4JWGlRLVleU9zQM3TQZZ_vou0OZBrE7C8k

On ILL the fact is Keith was so young he couldn't be understood. Eventually the older actors started repeating all his lines. As he got a little older the problem resolved--by the end in CT and in the Comedy Hour he was fine.

Chances are he came in for some criticism and caused some retakes on ILL, making it less "fun" for him than TAGS.

I'm glad Keith found his experiences to be "wonderful." A quick online check reveals he was even older than Ron Howard than he'd thought: December 1, 1950 vs. March 1, 1954. I find that age difference pretty surprising.