There could be a number of reasons why the free market, or the Fed would decide 10% is too high. Could be that the issuer has become more creditworthy/less risky. Or in the case of when the Fed decides, it’s about making the cost of money cheaper to have a more liquid economy.

As for you 2nd question, the price of bonds and the coupon rate have an inverse relationship. If the price of the bond goes up, then the coupon rate goes down and vice versa. And the reason is bc the coupon (the fixed stream of income) doesn’t change. So the coupon is fixed, the price goes up, that means now you are getting less of a percentage from the face value of the bond.