But I think that this is quite normal and even logical. Top boxers fight once a year (at best) and not every fight is interesting. It is difficult enough to be satisfied with such rare events. Unlike professional fights, show fights are almost guaranteed to provide entertainment and they can be held at least every week - literally as much as the public is willing to pay with their attention and money. The pandemic has popularized this type of entertainment, but this does not mean that at the end of the pandemic, the public should cool off for such fights.
There are still fans who wanted to see their former champ to fight inside the ring and promoters are taking advantage knowing that there's still ticket sales that they can convert each time they offer this kind of events. Even it's no longer the same crowd as with the pandemic but they can still collect a good amount of money for this kind of fights.
It's on the fans and the gamblers who are still thinking that they are willing to take that gamble and enjoy the fight.
You are right, and it doesn't really matter what a popular person does - his followers will look at it with interest anyway. If you take twitch, then the most popular streamers, no matter what they do - from just chatting to playing some kind of stupid game (not interesting to anyone if you don’t take into account who plays it) always collect a huge number of viewers. Similarly with these fights - legends are always interesting, even if they have grown old and cannot be competitive in purely professional sports.