Thanks a lot for sharing this. It's a shame this is not mentioned clearly, if at all in the introduction steps of Google Cloud Functions.
The team went out of their way to make a shiny "hello world" example but left out the crucial step to use Express Routers which is recommended in Express 4+
They probably assumed that customers like me would either
a) Write hundreds of lines of code within there generated index.js (which did not mention Functions Framework btw)
or b) go back in time and use Node Js 8 and Express 2 or 3 that did not advocate for Routers
I wasted yesterday on this.