Every web app starts out fine, the tabula rasa of an unwritten BODY. But sooner or later you need users. And a million other things which live in trees.

Also: email.

And that layer between the controller and the database where things like fine-grained access control goes.

I'd like to have an admin, please.

Eventually, web apps grows up. And while a larger framework with solutions and conventions for all those grown-up features may not necessarily be fun, it can certainly be useful.