...commitment to The Beverly Hillbillies

https://www.metv.com/stories/max-baer-jr-was-forced-to-refuse-a-guest-spot-on-this-popular-sitcom-because-of-his-commitment-to-the-beverly-hillbillies

Creator Paul Henning said that the guest spot would have "destroyed" Baer's believability as Jethro.