few libraries

hello everybody
as all of you know, one of the most important reasons that we use frameworks is simple and fast web app development 
and the framework must have the all needed classes
I think the only class that every web app needs is user management class
registering
logging in 
logging out
assigning to a group
etc.
but Codeigniter doesn't have this class
of course I searched and found "Ion auth" 
but my question is why codeigniter doesn't put such this important and useful library in its core library ?
it was and example
there are many other examples like "REST API" library
regards