The thing is: Where is the competition though? Considering that most IT departments don't want to spend an extra dime to do consumer-grade software engineering to do any extra integration there is no significant competition to Microsoft 365 and Active Directory.

Google Workspace is the closest but it isn't even in the same playing field when comes into advanced integration. Microsoft killed all of its competition in 90s and early 00s. Nobody stopped them. Nobody applied antitrust law. Now they have at least a decade ahead of everybody else.

Any competition should have to spend quite a bit extra money to just move all the integrated apps (SAP, Salesforce, CAD software, Exchange extensions) to their environment. To repeat my point, most IT departments want to spend a whole 0 on developing / engineering integrated solutions and developing those require some millions per year at least. Microsoft sells these stuff as low as €20 per user depending on the contract.