You aren't entitled to infinite support. You are entitled to keep using the thing you paid money for. If the publisher can't support the online service, they're obliged to make the game still playable by either releasing server code or offline modes.

If you sell a product for money, you don't then get to later take the product away and keep the money.

It's not endless support but more "Don't stop me from playing the game". For example, win xp is no longer supported. You can still use it.

For a lot of games the current situation is essentially the same as "The OS is no longer profitable enough, so the developer prevents you from using it"

You still can sell X months access, if that's what you plainly state is being bought.

I don't think you could sell "for as long as the developer supports the game" specifically, since that'd be an illusory promise (no actual obligation if the product can be revoked immediately), making the contract unenforceable and the customer entitled to restitution (a refund).

"infinite support" is pretty much just "leave the customer with the product they bought working". There doesn't need to be any ongoing costs.

Increasingly it seems like the fact that the game needs support for online components was invented in order to give it an expiry time.

Gamers simply don't have the impression that they're getting value from the "support," rather than getting shafted come end of life.