Since players can post reviews even during Early Access I think most developers try and keep the game largely playable.

Releasing a huge patch with potentially massive bugs would invite a lot of review bombing so devs create EXTRA EARLY ACCESS branches to test stuff out before hand.

Basically, people expect Early Access games to be completely playable and will throw a ♥♥♥♥ fit if it isn't so devs are forced to do stuff like this.