[nudq]

Going on title and comments only, sorry, but why does "it's genetic" count as an explanation for anything?

An explanation for this would need ecology. Why is it beneficial for some of us to need less sleep, but not for all of us? What are the trade-offs? It seems like needing less sleep has no downsides. Is it a novel, all-beneficial mutation that just didn't have the time yet to sweep the population? Or do short sleepers experience serious downsides?

There is no explanation in "we found a gene for it". Pretty much every personality difference is genetic, that doesn't explain why such differences evolved, or persist.