I ran servers with 100000s of sites/applications per server and indeed php made that possible. I had a complex setup with jails/chroots and selinux and some customizations to the mysql, apache and php source to make sure users couldn't abuse things. With nodejs or whatever, we would've ran a huge loss, now we ran a nice profit.

When people go on about environmental issues and such, I cannot help to think all the useless cycles spent by 'modern software'. FaaS helps I guess. But that is not really unlike CGI; with my old setup it is actually practically the same but mine was less flexible (php only).