My guesses:
-no one really cancels their security vendors since security budgets don't shrink
-they have a big moat so their customers won't be able to leave them
Companies already trust Microsoft, they buy Windows, Office, Azure.
Why would they bother with a 3rd party here when the low effort low risk solution is to pick the tool made by the OS vendor. I.e. windows defender
It should be a nobody gets fired for picking IBM situation. How did this random place get so much credibility that people trust them over the manufacturer?