In a way we kind of moved back to CGI, it just happens we call it serveless nowadays. :)
Irony is that it's most useful for hobby projects. In production I'd not use it.
That is one way many agencies have reduced their delivery teams, a bunch of cloud products tied together, and infrastructure is someone's else fault.
And because of serverless, there are frameworks optimized for low startup time, and those frameworks would probably work pretty well for CGI too.