The simplest answer: the Senate overweights rural voters, who in turn hate government spending and big government. Until the Senate is representative of the US population, we will never have sweeping programs like this. Even if the Senate is fixed, the supreme court could likely strike down any legislation that's too progressive, since it's now 6-3 conservative lean due to the Senate and McConnells robbery of the Garland spot. It's a messed up system, sigh.