Its not the basic mail and calendar functionality that drives large business to Microsoft (and to a lesser degree Google). It's really not anything that a normal user would see in an average role.

Email in a large organization requires things like central management, compliance with retention policies and other regulations, data loss prevention, encryption standards, auditing and ediscovery capabilities, etc.

Yes and they keep blocking features in Firefox on Linux. When I change the user agent to match edge on windows things suddenly work fine.

When it's set to Firefox attachment uploads don't work and ever morning it jumps to "please wait while we're signing you out..." when i never asked for that. When it thinks it's edge it just stays signed in.

Not to mention the huge amount of telemetry I need to block with ublock origin.

You don't want a drop-in replacement for each service, you want one for the entire system.

Microsofts advantage is ActiveDirectory integration. Centrally managed users and machines, every user, every application, every service authentications through the AD.

Organizations opt for Teams all the time, because it's part of the package and fully integrated. There's no reason they couldn't pick something else, but why deal with it when Teams just work (sort of).