Very rarely would he allow for special guest stars to appear as a one off character. I know that the Honeymooners cast always comprised actors that were regulars to The Jackie Gleason Show. And they were apparently, very good at playing multiple characters, which is what Jackie liked.

I feel like somebody associated with the show addressed this at some point. One possibility is that Jackie thought it would be distracting. There were, of course, guests like Frances Langford, The Dorsey Brothers, Jack Benny, and George Burns and Gracie Allen's son, Ronnie in the 50s. Many others showed up during the Hollywood episodes of the 60s, including Langford again.