The point is to launch new jobs and new races 1-2 weeks prior the actual expansion release.
As i mentioned earlier, this will allow for players to go into endwalker with their sage / reaper lvl 80 from the get go without wasting 2-3 days while everyone else is having fun in new dungeons / zones.
Also, let's be honest, everyone will start with early access. EA is here to justify the server instability at launch and potential major bugs that will be fixed right before the "actual" relase