There is a level between installing wordpress plugins and creating state of the art massive scale infrastructure. And its likely where most developers sit.

I work on a project management application. Its pretty much entirely custom code with little external libraries but it also requires very little computer science theory. The problems I face are less "Find the fastest way to search this datastructure" and more "This code was designed for a legacy model of the system, how can we replace it with something modern without spending months on it"