Doesn't Skype just come prepackaged with Windows now, making the "more people use me" argument the same as Internet Explorer's? In the end, more people using something doesn't mean it's better, other factors can but not just that.
@matosh While true, this usually comes down to the same reason a lot of businesses still prefer to use fax machines over email: not wanting to change things up and potentially complicate it since people would have to learn something new. If they're using Skype for Business, they're going to have to change to MS Teams or another service eventually because it's not getting updated anymore and errors and bugs are piling up.