Why Zoom did so well - initially I tried Google Hangouts, but there were lots of dropped connections and frozen screens. When trying Zoom, it worked much better. I think other video-in-a-browser services have the same problem (Google Meet, MS Teams, Facebook etc) whereas Zoom has a somewhat old-fashioned app that needs to be installed (it can also run in a browser, if preferred). BBC article supports my findings of 9 months ago "...and strong underlying technology that deals well with sub-standard internet connectivity"