My personal theory is that Microsoft probably thought Apple would stay on 10 forever, but with M1 macOS moved to 11. 11 > 10...
Edit: https://www.extremetech.com/computing/191279-why-is-it-calle...
this one goes to 11
It happened with a lot of other software (Firefox vs Chrome is just one example).
Version number envy?
We joke but these are marketing names intended to make a big deal of a large batch of features. With today's continuous delivery (ie. incremental upgrades) this is no longer needed, at least not for technical reasons. But from a marketing perspective, it provides the opportunity to generate buzz in the news with "OMG best version yet"-style announcements.