The UFCW also helped facilitate two tier wage systems where new workers get compensated significantly worse than existing workers, so this isn’t the first time they’ve helped disenfranchise the members they supposedly represent.
Consider what the Union goal is - expansion of membership and increased funding/power/leverage. Uber’s goal is brand-washing. Fighting employment law is a cynical win-win for the Union and Uber in this instance - member welfare be damned. Tells you a lot about the intentions of both the union and employers.