Because it doesn't need them. There are more polished versions of those features elsewhere, and they can be composed easily with Negroni as they all use the same interfaces.

I thought your point was about the necessity of magic in a web framework. The most magical thing about Martini was its dependency injection approach, which Negroni provides in an idiomatic way.

Unless you're saying that it's the magic that makes a framework a framework, as opposed to just a collection of libraries. That makes sense, because the magical approach of Martini (for example) does, in a sense, lock you in to using Martini. This makes it more like the monolithic web frameworks you mention.