I think the reason for that is less that they didn't want to do it and more that they hadn't polished the mechanisms for it.

I've said before that the analogue for these sorts of games is arcade games - where you had to put in currency per unit time of enjoyment, and they had to try to guesstimate play time versus amount they're willing to pay for it and then would go in person to "test" arcades with early versions of games to see if they were wrong.

The internet reduced that feedback cycle to minutes, so we speedran evolution on it.

TBH, I don't see monthly fee games as even in the same category of concern - at least, not in a vacuum. Games with microtransactions, yes, absolutely, but that's true whether it's nominally a pay-once game or not, I think.

I said in another comment, I don't hate the idea of allowing microtransaction/gambling-style mechanics in games as long as they can't involve real currency on either side, if children are the market - not because I think it's great for kids, but because I think you're not going to manage to ban everything that's the same addictive "shape" as those, and allowing people to be exposed to that in a venue they care about, but with foam sword padding so you can't blow actual money on it, is probably a reasonable risk/reward balance.

(You might reasonably argue that this is just going to lead to kids being primed for addictive behaviors as adults, but the only thing that's going to help that is being mindful about it, e.g. education, and nothing short of people the kids respect reinforcing that is going to change that whether the games allow this sort of soft pain or not...and being exposed to something like Vegas naive or primed is going to, I think, have the same outcomes either way if you're not mindful about it.)