Municipals and Insurance

Why does it seem that bond insurance seems to be mostly associated with muncipals instead of other types of bonds? Also would the yield a municipality would have to pay to issue non-insured bonds be that much greater then the yield + insurance payments of an insured issue?

I don’t know exactly but I always thought that it was because it’s difficult to diversify away risk in muni’s without getting rid of the tax advantage so bond insurance pays for itself by taking away regional risk while preserving tax advantages. I guess in corporate and other issues diversification takes away the need for expensive credit insurance. Edit: Oh and for the second part the answer is supposed to be yes, but I’ll bet it’s sometimes no.