Because nobody wants to touch it with a ten foot pole.
There are basically two ways to get interest rates back up. The first is that you just do it, and nothing else. We've discovered that doing this at anything faster than glacially slow when people are as leveraged as they currently are causes the world to burn. If interest rates doubled over a short period of time, the thousands of dollars people are already paying in interest would also double, and eat all of their disposable income and then some, requiring them to borrow even more at the now-higher rates in order to make rent. Bankruptcies would follow. The higher interest rates would make it harder to get a huge mortgage at current housing prices, so housing prices would crash. People have borrowed money to invest in stocks because the return on stocks has been higher than the interest on money, and raising interest rates tends to be deflationary in general, so you raise interest rates fast and the stock market crashes. At the same time as the housing market. Nobody really wants this version. It's terrible.
The alternative is that you raise interest rates against a backdrop of a series of pro-inflationary policies, that allow wages and the price of everything other than housing/healthcare/education to catch up and rebalance. And you need for people to pay down their debts so that interest rates can rise without bankrupting everyone, which means they need money to pay them with. But money comes from two places. One is debt -- banks create money when they make loans. But we can't use this one because the whole point is we need less of that.
The other is the government creates it. They need to create enough money for people to pay off their debts with, which destroys it again. That would be trillions of dollars. And then enough on top of that for wages to catch up to housing prices. (A UBI would actually be a great way to deliver the money to people.)
The banks would hate this with the fire of a thousand suns, because it would mean that the total amount of outstanding loans would fall significantly. In other words, their industry would shrink, by a lot.
So those are your options. Lots and lots of bankruptcies and a huge economic crash, or printing trillions of dollars for people to pay their debts with. Either way the banks are stuffed -- and they're the ones with the largest influence on this kind of policy, so they're firmly in the "kick the can down the road" camp of leaving interest rates low.
