You seem to have a very limited idea of what an adult finds enjoyable, if it doesn't have a spa or a beverage tasting an adult can't be interested? I also think you might underestimate how many adults-only groups visit Disney. When you look at parks with a lot of locals like Paris or Tokyo the majority for sure are adults only or local young adults with an AP. Probably the same for Anaheim?
Therefore also there are a lot of adults doing character meets. On my 10 day trip to WDW, adults only, we met in total 100 different characters. Going by some former Disney character actors on Tiktok, several of them claim to preferred meeting adults, because you can have a conversation and properly act and improvise. Cuddling toddlers is fun, but it gets uninteresting for the actor after a couple of hours.
Looking at the Disney cruiseline, there are usually more adults only groups than at the parks and there are more character meets to guest ratio (my guess) than in the parks.
Disney does this because they know how much adults love meeting characters. And they are not going to remove or adjust something the majority of their guests loves to do.
Because they will loose money if they do.
If they do, we miss out on great content like this:
Also, I do not think you can claim the park would be safer for families without only adults, as the majority of the abuse cases involving children, usually the abuser is a relative or someone close by. I would have to look into it, but I think the amount of times a child at Disney got abused, kidnapped etc by a stranger can be counted on two hands, maybe even one.