Because, just as the Bonanza, they tend to be "Doctor/Lawyer" airplanes

A C-210? Didn't think they had the same allure as Bonanzas & Barons for
the MD/JD set...

This insurance agent told me the 210 was a special case, I assume due
to loss rate. There are some companies that won't write policies for
210s at all. I just can't figure what it is about that plane that would
make getting insured such a hassle.