Short term paper pays interest because it’s issued by people who need short term money and are willing to pay for it. There’s no central authority setting its value, no objective criteria, no law of physics, just actual people choosing to pay for something they need. Same with equities, same with bonds. Same with money itself.
As I said even central governments don’t set the value of money, only it’s supply, people set its value. That’s why the currencies in Venezuela and Zimbabwe collapsed. The people selling things chose how many ZB$ they wanted to sell things for, and buyers decided how much they would pay, and it turned to be a lot because there was so much around.
Nobody needs you to keep money in a mattress. It doesn’t benefit anyone, so they won’t pay you to do it no matter how useful you think it is to you. An economy with a significantly appreciating currency is set up to incentivise not engaging in economic activity, not investing and not lending isn’t going to work very well because those incentives have to be paid by someone somehow. Why would they do that?