I'd argue that Teams is bigger than Slack because Microsoft pulled a fast one, exploited their monopoly, and included it "for free" with the rest of their licenses, rather than getting people to sign up de novo. The fact that it's worse in every meaningful way than the competition, yet far wider used, highlights the whole problem quite neatly.

We have to use teams because teams is free. Despite it being terrible. There was also a push for us to switch from Miro to Microsoft whiteboard. Until a senior manager actually had to use whiteboard and they realised it was terrible.

Don’t they “choose” Teams because it integrates with outlook/sharepoint/etc? That seems to be the case at my job. Basically, Teams replaced Skype.

Because of Office license lock-in, not reputation.

Part of it is rational, because they see lots of chaos/noise in the market while having to make too many decisions. Following the "best practices" only saves them decision-making time. Might not be the "best" in practice, but at least they don't have to examine a gazillion options that are available.

Teams is bigger than slack? Like, the executable?

Teams is an abomination; something to be cast into the fires of Mount Doom. Slack is miles better for everyday communication.

I agree its absolutely awful but Teams is far bigger than Slack, I'm not sure why you'd argue that.

My sample size of three large companies, two use Slack. Boom.

(I did move the goalposts from "deployment size" to "quality").