Falcon is a very lightweight framework. This can be noticed simply by looking at the dependency list: other than the python standard library, six and mimeparse are the only dependencies.
Falcon is designed entirely around building REST APIs. This helps a lot with it being lightweight and simple. It also helps developers take some design choices which would otherwise not be possible with a more general-purpose framework.
Being designed around building REST APIs and the fact that it's minimalistic with very few dependencies makes Falcon opinionated (you should build a REST API) and limited in scope (you shouldn't be using Falcon to build a news site, blog or ecommerce platform).