Following PSR standards doesn't make a framework less simple, and it has the benefit of making lots of middleware instantly usable by that framework.

Number of files isn't a useful metric because other microframeworks can be run without ever loading the router or any of the data storage classes. They could be run with less than 10 files loaded. And even then, it still doesn't matter because number of files just means number of classes, which doesn't say anything about the readability or simplicity of the code.