That's because that episode earned Gleason the highest rating he'd gotten in years; when it aired in 1966, he was having his hands full against "Flipper" and "I Dream Of Jeannie" on NBC. The "Honeymooners" revival, say what you want about it, did put Gleason back among the top-rated shows; he was even number one in the Northeast in 1967-68.
Gleason had known Jane Kean for more than 20 years when he hired her to play Trixie. He and Lew Parker (Marlo Thomas's dad on "That Girl") were a comedy team in nightclubs in the '40s; they worked with the singing Kean Sisters, Jane and Betty. Lew Parker eventually married Betty Kean, but Gleason never forgot them. Joyce Randolph, OTOH, while she may not have wanted to move to Florida, has said on more than one occasion that she and Gleason did not get along for reasons I don't know. Audrey Meadows did come back to play Alice in the '70s ABC specials, but Jane Kean played Trixie on those; Sheila MacRae was often criticized as being too glamorous-looking to play a downtrodden housewife.
Ironically, both Sheila MacRae and daughter Meredith saw their shows canceled the same year, 1970, as both Gleason's show and "Petticoat Junction" were two of the first three victims (along with Red Skelton) of CBS's attempt to "modernize" its programming. (I would include "Ted Mack's Amateur Hour," but he asked CBS to take his show off the air that year.)