I'm no UX expert but I'm going to claim it's because of the UX that Teams doesn't work for so many people, and I'm left wondering why Teams hasn't had a UX overhaul yet.
The other competitor to Slack is Discord, and if you remove the playful "gamer" elements I think it'd be a lot less jarring to people used to Slack, because they follow a lot of similar UX and design patterns.
At one point Discord tried to rebrand into something a bit more serious but it didn't work, but I think they should try again; create a Discord Pro or something like that, get the certifications, add SSO support, etc.
The other competitor to Slack is Discord, and if you remove the playful "gamer" elements I think it'd be a lot less jarring to people used to Slack, because they follow a lot of similar UX and design patterns.
At one point Discord tried to rebrand into something a bit more serious but it didn't work, but I think they should try again; create a Discord Pro or something like that, get the certifications, add SSO support, etc.