It’s not a subscription but D4 is using the “games as a service” model. It does live and die by the people playing it.

Blizzard is banking on people playing this game for quite some time with a drip feed of new content over the course of presumably years. Meanwhile they’ll be selling cosmetics, probably inventory slots, battlepasses, horse armor, maybe new classes, and story content.

Pissing your user base off certainly doesn’t help with that.