justus_
The trend gets accelerated because most new programmers start with javascript, or soon switch to javascript because they see it as the one language they can do "the most" with.
The fresh blood is, due to being new to programming, very explorative and curious about platforms and such drive the use of (back then) experimental tools up a lot.
I personally think that both PHP as well as javascript suffer from being designed not just with flat-out bad syntax, but also for a rather narrow use case and then being adopted widely for lack of widespread availability of other tools.
As a result they are used in places they were not expected to be used and for systems of scale that they were not intended to handle.
The backend of the future may run with node or it may run with PHP, I hope for neither. There are languages out there with more powerful and safer abstractions, with more carefully designed APIs and standard libraries that do not just clutter the global namespace, with usable import functionality from the get go and with type checking and -inference.
But that's just my two cents, I could be wrong :)
I also don't think your app would get more scalable. You might have less code overall in your app but how well documented is it? Is it as well documented as the frameworks? For whom one of the most important concerns is usability and making sure others understand the code? Overall I doubt your code would be very readable. Many people write awful code and I doubt there's a lot of in depth code review in most companies, requires too many resources.
Another point when it comes to scalability is interfaces. Interfaces to talk to other instances, interfaces for pluggable modules, interfaces for the database, interfaces to different frontends. If you want your app to be scalable and possibly distributed and/or extensible you need good interfaces and programmers are also notoriously bad at designing those. (That's why JavaScript is the way it is) The only reason why those of frameworks are somewhat workable, is because they made a lot of mistakes before and learned from it (mostly). Good interfaces require constant and incremental improvement. A maintenance effort hardly any company would like to bear.