Musk tried to operate DOGE, head of personnel Sergio Gor didn't like Musk's meddling, Musk lashed out at Gor, Gor pulled support of Isaacman as retaliation (citing donations to Democratic candidates despite donating to Trump's campaign), Gor didn't get permanent security clearance (June, unclear his country of origin, Malta says not from Malta, says he's from Uzbekistan when still Soviet), Gor assigned as India Ambassador last month, Scavino replaces Gor within the last week, opening for Isaacman nomination returns.
I'm sure there's politics with relationship to Alabama/Huntsville, but it was reportedly Gor and his feud with Musk that caused Isaacman's nomination to be pulled. Isaacman is Musk's preferred appointee. Isaacman being pulled was the cause of the Trump/Musk rift.