> You could easily migrate off of it tomorrow and everything would be fine.
Have you missed the news where multiple countries tried to do exactly that and it took either multiple tries or was abandoned? This is very deeply engrained in government and corporate networks (For good reasons like support, backwards compatibility, staffing etc.) but it's not something you can change over night like replacing your parents computer with a Linux version with a similar GUI and hoping all will be fine.
It's very difficult to do it smoothly with no downtime, but all it takes is one emergency for the existing workflows to be thrown out. Companies suffer emergencies and data losses all the time and nothing ever actually happens, they get over it.
Have you missed the news where multiple countries tried to do exactly that and it took either multiple tries or was abandoned? This is very deeply engrained in government and corporate networks (For good reasons like support, backwards compatibility, staffing etc.) but it's not something you can change over night like replacing your parents computer with a Linux version with a similar GUI and hoping all will be fine.