The "Microsoft Tax" is often cheaper than the "Linux Engineering Salary." While Linux alternatives exist, they require "assembly"—integrating LDAP, Kerberos, DNS, and config management (Ansible/Salt) to do what AD does out of the box.
Most businesses don't want to be in the business of maintaining their own identity infrastructure. They want a utility. Between Group Policy’s granular control over the endpoint and the tight integration with Exchange/M365, Microsoft has created a "sticky" ecosystem. I've tried the "DIY" route with Linux mail servers, and the friction of maintaining deliverability and security patches manually is a nightmare compared to the "it just works" nature of the Microsoft ecosystem.
I am not a system admin, so maybe this is a crappy take.
Crimson Stained Lands is a Multi-User Dungeon (MUD) featuring races such as elf, human, dwarf, orc, and minotaur. Play as one of our many classes including assassin, bard, healer, mage, paladin, ranger, shapeshifter, thief, and warrior.