Why though? Why is that requirement there? Okay, it's nice for me to sync everything and have a seamlessly integrated ecosystem. But what if I have one device and just want to use Word on it and that's it?
It's a subscription, so they have to know it is you to know if you've paid your dues or not. MS is a bit sneakier though as they will allow you to open a document and make changes, but if you are not current in your subscription fees, they disable save functions. Been caught out on this a couple of times.