I work for a company with thousands of employees and we used Slack in our small team, we chose it because the majority was already familiar with it (I voted for Mastodon) and we spent part of our team budget to pay for it
When COVID hit the fans and we started working from home, the company chose Teams as the collaboration platform for all of us
I don't love Teams either, but I honestly have to admit that the voice/video calls are incredibly reliable even on some shitty DSL connection I found myself using that had a packet loss ratio around 50% and no other alternative worked
For everything else Teams is worse than Slack, except for the integration with the AD domain and sharing documents with colleagues that never used anything else than Windows
On average Teams is as good as Slack and for casual users that only use chats and calls there is no difference at all
I can see why companies are switching to Teams, they have been MS customers for years and Teams comes bundled, it's one less contract to sign and one less vendor to start a relationship with.