Subscriptions are a sustainable way to do it, or so it seems from the games that have lasted 20+ years with decent player bases. I get where you’re going though, cash grabs are common in games nowadays and making a game a live service is a great way to do more monetizing, but it isn’t necessary.
I agree that it’s bittersweet to see a game change over time, and that is definitely a trade off of MMOs, but imo it’s not a total negative, a game having visible history in the world, when done well, can be a benefit.
Live service games aren’t all bad, imo mmos are a good example of a good live service game, I would never have the same enjoyment for RuneScape for example if it were not a live service game, there is a level of authenticity to achievements given by it being a live service. Also it’s a little disingenuous to say non-live games get updates too implying its equal when a good live service game can put hundreds of hours of content per year into the product without worrying about when they would need to release a new game or paid expansion to continue being profitable.