Let's consider how dwarves are portrayed in D&D 4E: Stereotypically short and strong with a penchant for building and craftwork, yet they live above-ground, without any sort of ability to see in the dark, and were once enslaved by the giants. Let's riff off that. Modern dwarves are, in fact, a slave-race bred by giants for manual labor, selecting them for strength, hardiness, and ability to do tedious work (and losing darkvision in the process). They eventually revolted and won their freedom, spreading out into the world.