It is because Calibri was made with reading inclusion in mind (no thin slanted lines) and the current office actively working to exclude as many people as possible for no obvious reason other than pettiness.

Although, maybe they want to start writing in latin one day again too, so to exclude even more people (like the old days when only the elite were able to read relevant sources).

It’s because it’s got Roman in the name, isn’t it?

also Calibri is a humanist sans-serif font