> And they'll be paying Microsoft for licenses as long as they have Active Directory, right?

They'll be paying long beyond on-prem AD as well. EntraID is becoming the new identity system. If you're already on E3/E5, you might as well make use of it, and making most use of it means being stuck in the whole Microsoft ecosystem.

Why bother looking for alternatives, even if one particular product might be better, when Microsoft gives you literally everything at at least a mediocre level, for one price and pre-integrated.