Why might the yield to maturity on, say, a BBB-rated municipal bond with moderate default risk actually

Question:

Why might the yield to on, say, a BBB-rated municipal bond with moderate default risk actually be less than that of a U.S. Treasury bond with no default risk?

Maturity
Maturity is the date on which the life of a transaction or financial instrument ends, after which it must either be renewed, or it will cease to exist. The term is commonly used for deposits, foreign exchange spot, and forward transactions, interest...