That’s because Dems are capitalists and always have been. Even when they had the support of powerful unions it was only the class collaborationist unions, never radical unions. The Dems were social democrats when there was a strong socialist movement that threatened capital interests, making it necessary for the capital owners to co-opt and redirect it. FDR implemented his reforms in the interest of preserving capitalism, not for the benefit of the working class. He saved the ruling elites from their own hubris, and they hated him for it.