Democrats promote these irrational increases in the minimum wage because of two reasons:
First, and most important, most union contracts are indexed against the minimum wage. Increasing the minimum wage provides all of these union employees automatic increases without any additional bargaining.
Second, it provides an opportunity for their favorite past time - class warfare.
Fortunately for them, most of us have been so dumbed-down regarding anything of an economic nature that they get a complete pass although they destroy the very people they claim to champion. They know this and couldn't care less if they benefit politically.