For decades, the Nevada Democratic Party was ruled by Harry Reid and his proteges, a bunch of tough centrists who waded through trade-union bureaucracy and greased a ton of palms to get every vote they could. When there was a better than fifty-fifty chance of the Democratic Socialists winning, the NDS transferred $450,000 from the NDS coffers to the Democratic Senatorial Campaign Committee, where Reid protégé Catherine Cortez Masto is running for Reid's old seat, and bailed.
While it can most certainly be seen as a case of sour grapes over being trounced, them fleeing the NDC is probably more about avoiding change. Grassroots fundraising and fundraising via knowing the right people and trading favors are two very different animals. So they scattered to other places within the larger DNC umbrella where they'd still be appreciated for their length of service and extensive contacts list, rather than having to change to being appreciated for how much fervor they can generate from common people.