The convenience and business sense argument could make sense if the value of a communication platform was small and close to its cost. But it's not. Similarly as it doesn't make business sense to rent the cheapest or easiest to lease office exactly because a good office to your company is more valuable than its cost.

People hate Teams/Office because it's so low quality, effecting a large drag on communication. It's also incompatible with effective organizational culture (eg calendar has hardcoded top-down management assumptions, information is siloed to only meeting participants, cooperative doc editing corrupts and loses data, sharepoint is a psychological horror game etc). Its usage is a useful signal about an organisation though.

And of course it's a giant red target from security POV, as is obvious the headlines on the MS phishing epidemics and regular news on the gaping slapstick level security holes ([0] [1] [2] etc) in the load bearing part of company security (identity, and email password reset channel).

[0] https://www.bleepingcomputer.com/news/security/new-critical-...

[1] https://www.hkcert.org/security-bulletin/microsoft-exchange-...

[2] https://digital.nhs.uk/cyber-alerts/2021/cc-3977