Zoom is basically a respin of WebEx. Teams is a bunch of modules bolted on to SharePoint and Exchange. A “team” is an exchange artifact, the voice and video is a module and the rest is a SharePoint front end.
Zoom is a better value if you need features beyond the base teams. You pay a simple fee and get the whole shebang. With Teams, you may need different SKUs, including Azure AD, etc to get the full feature set. It’s a funnel to E5.
For one thing: more than 120000 congregations of Jehovah's Witnesses worldwide started paying for a Zoom account in early 2020. As far as I know, most of these congregations still pay for Zoom accounts until now.
Call quality was not the factor. It was that zoom was easy for people to use, no download required, just click a link and enter your name and you’re connected. No logins or downloads so old people could actually work with it.
I never used the zoom web version, but for the client: it simply worked. Getting videocalls with WebEx always was a pain, where it was noisy, video hat issues ... switching to Zoom was day and night. Suddenly doing a video call was a click and it worked.
Zoom is a better value if you need features beyond the base teams. You pay a simple fee and get the whole shebang. With Teams, you may need different SKUs, including Azure AD, etc to get the full feature set. It’s a funnel to E5.