But, really, why they did? Since it's canon on Disco, this breaks all excuse that Nomads have on their hatred to humans. AFAIK, Nomads are hostile to humans because noms think that the Sirius is bequeathed to them by Daam K'Vosh (and the proof to their claims is yet to be discovered, maybe K'Voshes left their legacy to humans or to whoever will be smart enough to crack the musical key first?), and the humans have conquered their homeland. But the destruction of Sol had happened before sleeper ships arrived into Sector (or even pierced the nebulas bordering it), thus, we have an act of unreasonable aggression from K'Haras.