It's more of a tradition, really. There are plenty of other formal fonts out there to use, but Times New Roman has been the standard for that kind of thing for decades.

Microsoft has changed the default font in Word with one of the latest updates. Instead of Calibri for normal text and Calibri Light for headings, the fonts Aptos and Aptos Display are now preset.

When you send a Word document to someone else, you expect it to look the way you intended. But your intended fonts don't always show up on your recipient's screen.