Because Amazon and Walmart, as the giants they are, aren't hurting for cash. If you're a small time vendor or buyer, those 30 days could be the difference between eating tonight or going hungry. Meanwhile. Amazon and Walmart could just pay it out of their reserves early and Jeff Bezos isn't going to go hungry. Also, why would prices go up?

Yeah, and? Redistribute all the wealth that goes to the stonk market to the people. Henry Ford figured that out a century ago - for a healthy economy, you need people to be able to afford stuff!