Because in request scope is easy to do with Web API
Regardless of what types of applications you are building with Web API, sooner or later you will run into a situation where you need to scope certain dependencies to the lifetime of a web request.
Examples of these types of in request scope dependencies could be loggers, unit of work implementations, NHibernate session, RavenDB session, Mindscape Lightspeed UnitOfWork or many other. Fortunately, this is very easy to do with Web API and an IoC container.
More after the jump.