Root bones and hips

I’ve been playing with several automatic riggers, and they all have one thing in common: the hip is always the root bone. Now, obviously plenty of rigs have what seems to be a copy of the root bone near the feet, but that’s all it is, a copy.

So, why is it so customary to lose movement of the hip to have a root bone that could be anywhere else? And how to make it so the hip work solely as a hip, while having a root bone at the base of the model? I assume it has something to do with parenting.