Then I presume you never had the misfortune of using Skype for Business?
We used this prior to Teams, and in comparison, Teams is great. I'm guessing a lot of Teams users come from Skype for Business, so they are really happy with the improvements.
Skype for Business was incredible next to Teams. Lightweight client (even though it was WPF), developer SDK that actually provided basic chat functionality, notifications that didn't automatically get lost in the scrum. I miss it a lot.
The server infrastructure was a bit of a shitshow, if you ever had to maintain an on-premise deployment, and it must have been a complete clusterfuck to run the Skype for Business Online SAAS service they were offering. So I can understand why they did away with it, but I'm still very irritated that this many years into Teams, it's such an unfinished mess...
SfB only did the non-persistent chat and A/V calls portion of Teams and is really more like a VoIP PBX. SfB calls still have better audio quality than Teams today - I'm guessing they've optimized bandwidth down to meet a "2/5 star rating" ("technically intelligible").
We used this prior to Teams, and in comparison, Teams is great. I'm guessing a lot of Teams users come from Skype for Business, so they are really happy with the improvements.