To make use of the materials and other benefits the system does have; the same reason we settle such places on Earth.

> Moving nontrivial amounts of mass around the universe is extremely expensive.

This amount of energy is a smudge on a ledger in comparison to the energy even a solitary, planet-less red dwarf puts out in its lifetime.

Unless we develop a method for fusing the materials we need from hydrogen and helium, the only chance of becoming a type III civilization is to learn to move mass around and make these trade offs.