Policy difference not partisan squables or payback for supporting his opponents. Most Democrats feel Unions are important to help workers (union and nonunion) earn more.
Democrats believe that unions help keep wages high and are good for the economy.
If Musk wasn't anti union he probably would have been invited. I say probably because of Teslas issues with racial discrimination
As for the claim that Tesla has racial discrimination issues—that’s a distortion. Nearly every major company gets hit with discrimination lawsuits because civil rights law has been weaponized to make that outcome nearly inevitable:
https://www.richardhanania.com/p/wokeness-as-saddam-statues-...