Bell Labs had a monopoly, as part of Bell Telephone, which was (AFAIK) granted exclusive right to provide telephone service. Microsoft does not. AFAIK, Xerox never has had a monopoly.

Having a large amount of marketshare != a monopoly.

Lots of people insist on using the term for both things. I don't know why. But even if you are one of those people, surely you will see there there is a fundamental difference between those two things.

For the sake of this discussion, it would be necessary to differentiate between them.