Why was that? Why no appearances from other Dick Van Dyke cast members?

Why was that? Why no appearances from other Dick Van Dyke cast members?
I think Mary Tyler Moore was trying to establish her own TV identity with TMTMS so she and her husband Grant Tinker made the decision not to have any TDVDS cast members appear on the show. Several people who had worked behind the scenes on TDVDS did direct episodes of TMTMS though. They are Jerry Paris and Alan Rafkin (who also were directors on TDVDS), John C. Chulay (assistant director on TDVDS), Marge Mullen (Script supervisor on TDVDS) and Jerry Belson (a writer on TDVDS).

This is a similar situation to Little House on the Prairie.

Michael Landon's TV father from Bonanza, Lorne Greene, didn't appear on LHOTP. ML said it was because LHOTP came on not long after Bonanza went off the air and some viewers might mix the characters up. However, Lorne Greene guested on Highway to Heaven because by then more time had passed.

I guess that does make sense....although a brief cameo from say Rose Marie Or Morey Amsterdam would've been epic!

I would have loved to have seen Richard Deacon as Mel Cooley looking for a job at WJM!

I think the only TDVDS star to appear on TMTMS was Jerry Van Dyke. He played Mary's boyfriend, Wes, who was trying to make it as a comedian. Oh, and Jerry Paris did direct an ep or two also.