Because I cannot affect Bastion, a PC is now allowed to commit all kinds of atrocities and, as long as they can flee to their Bastion. As I have said, a PC could now slaughter a whole village, piss on the king and kidnapp his daughter and, as long as they flee to their Bastion, escape consequences, because the DM is not allowed to interact with the Bastion at all.
And if you are saying that Bastion is so abstract that fleeing to it is impossible, then that's even more immersion breaking. There is a place a PC can build to live in, but it doesn't provide most basic benefit a place to live does, shelter. There is no way if a PC declared "I'm fleeing to my bastion and hiding until it's over", that I would not come looking like a railroading jackass for saying "You cannot, Bastion cannot provide you shelter". The way you are describing Bastion it becomes a video game menu with list of bonuses, that literally refuses to be a physical place in the world, it primary purpose being to just break the immersion and remind the player this is a video game, not a living, breathing world.
EDIT: And the topic of followers is the same thing. I am not allowed to have those characters react with disgust and horror to anything a PC has done, even if it's like slaughtering Village of Women And Children, Edmonton. If the PC says that his followers are all an order of righteous knights but doesn't want them to react a way righteous knights would to an act of evil, I'm supposed to roll with it because those aren't NPCs, just abstract numbers to cheer on the PC. It encourages murderhoboing by banning me from making player actions have consequences and it's a giant "IT'S JUST A GAME BRO!" sign that ruins all immersion-building efforts I've made.