If you can buy a game, play it for 100h and them hand it off to somebody else who can do exactly the same, with the publisher/developer/store are getting nothing from those transactions, they are quickly going to find another business model. There is no degeneration like there is with physical goods. There is no reason why anybody would prefer new.
And while publishers only lose a potential sale, vendors like Valve actually have to service a new customer (bandwidth, save storage, etc) without extra pay. They're not going to go quietly here.
And that will quickly turn into publishers and vendors both ceasing to sell software licenses. You'll still pay full price, but you'll get 100 days play, or a few years for a multiplayer. Or membership services like Origin Access. Or straight up gaming as a service (eg Stadia).
So while this is great for owners of existing software licenses in the EU, we shouldn't celebrate this ruling. We're about to own even less than we historically have.