MS lives by corporate contracts and there are a lot of very powerful US companies that will roll over if Trump barks - if MS had already fled the US in a legal sense they'd definitely be in a better place but trying to leave during this administration would cause Trump's ire to focus on them and likely cost them an immense amount of money. I don't particularly like MS and both office and windows are declining in quality quickly so I wouldn't be opposed to the move but... nothing would sink that ship faster than losing a bunch of large US contracts as Trump toadies demonstrate their loyalty by bravely switching to alternatives.