With each trip taking an average of 15 minutes, that’s about 200k concurrent, live sessions. Each session has at least two participants, so 400k live users any given second. I imagine their spikes are significantly higher than their slow periods, too.
Well sure. And I've worked on software run by ISPs that have had more than 4M concurrent active sessions. Handled by something like 20 machines. Yes, they probably have way more overhead per session, but it is still a really high amount of servers.
Now, granted, 2021 is probably down on that further but it's still a lot.