Online activation requirements. Physical media going away is really just a symptom, DRM is the actual issue. Games have always been just a license, what changed is that the licenses are no longer transferable and irrevokable. (They might even still be legally irrevokable, not sure, but they can just shut down drm servers and you can’t install).

Ofc DRM-free steam games or GOG games etc. aren’t transferable either, but the main issue for most people is clearly that they might lose access.

Consoles could just include a feature to back up game install files to USB storage or NAS and losing disks becomes irrelevant, but DRM will always fuck the customer in the ass.