Betty has definitely cut back, but considering how much she had appeared in recent years, who could blame her? I know she has limited mobility these days.
Barbara is hardly that old herself. She had a nice career, although I suppose appearing on The View can be hard on someone mentally.
Bob still seems quite sharp based on the video of him in Perfect Bid. His face appeared quite red though. I wouldn't doubt he has limited mobility as well. Perhaps the TPIR train could bring him out, or he could be escorted by a model. Bob may also be aware that despite only hosting one game, then appearing at the end, the audience was more than elated to see him come out the big doors... the applause grew MUCH louder when they realized it was him and not Drew. He might be concerned about stealing the show from Drew again.
When Monty came back to Deal in 2010, it was amazing to see how sharp he still was, and it was very entertaining to see him for a full week... a few years later, he came back again, this time with Carol Merrill, and while he was still sharp, you could sense he was a bit winded. That was his last appearance on LMAD, and he only appeared again on Game Changers, looking quite frail and his voice was weaker too.