Why?
The banks keep your money. They charge fees. They loan out money at a profit. Many people who are retired or nearly so have saved an amount such that 4% interest (or so) would supplement their retirement, and that interest would be money pretty much completely spent in local economies.
Now you have a model where banks can profit from your money but not have to give you part of the return. But still their executives and largest stock holders get very nice returns and bailouts if they mess up. If you don't have a large enough balance, they'll charge the saver a fee for safe-keeping of the money.
It's not a sustainable model. Older baby boomers and retirees have mostly prepared for the future. How are most younger people going to be anything but indigent when they retire?
By keeping interest rates artificially low, the government penalizes savers by offering them 0% on their money and rewards borrowers. It is considered a stealth tax on the middle class.