Answer:
To compensate for the risk that they will receive less than promised if the firm defaults, investors demand a lower interest rate than the rate on U.S. Treasuries.
Explanation:
Investors are risk averse, this means that they will always prefer those investments with lower risks. Since US treasuries are considered the safest investments, Â they are used to calculate the risk free rate.
When investors invest in other securities (not US government) they will always demand a higher return because a private entity or even a state or local government can default on a their debt. That difference between the return yielded by a US security and the return from any other investment is called the risk premium.