What do you think powers the InterNet that you're connected to right now? Multiuser systems, running applications under different logins. Even the much hated systemd brought physical multiuser computing back to GNU/Linux.
It kind of reminds me of shared hosting providers without root access. Sure they exist but really have been overtaken in a big way by virtual private servers... That's what I mean by they seem going out of style.
I doubt there is a top internet company around that makes a unix account for each web user. That would be an antipattern...