The real reason that companies don't all do this is that it involves a nonzero amount of work to convert a game to work without the live service it originally depends on, and because there's no legal obligation to do so, most companies just... Don't care enough because they're onto the next thing. For example, Helldivers 2 chooses what missions and modifiers exist based off of the meta war decided by a lore master. To convert off of live service they'd have to program some intense stuff to get it to generate random possibilities that act like a meta war independently and such, which is not trivial.

It'll never be widespread until it's mandatory because it's asking the company to do work to allow players to continue playing a game when the company would reaaaally like it if you were just playing something else they make instead, something you might spend money on.