They can just stop giving them new GPUs, undercut their API prices by a significant margin(they have the same models!), set up transitioning pipeline, etc. They can cause OpenAI A LOT of pain if they want to.
Why would they suddenly stop acting in the best interest of their business?
Imagine the headlines, "MS Guts OpenAI for Putting Ethics over Profit." That's how it would spin, eh?
Apologies.