One of the main reasons why many homeowners did not have flood insurance before the advent of Hurricane Katrina in 2005 was:

C.Homeowners thought that the likelihood of a flood was too low to justify buying a flood insurance

Explanation:

Most residents in Louisiana did not believe that Louisiana could be flooded in the event of a hurricane. Indeed after the hurricane, various interviews showed that Realtors even advices home buyers not to worry about Flood insurance. Most residents usually got Wind Insurance.

The reason for this was that in past Hurricane, Louisiana had been spared of floods because there was a lot of highland. The flooding therefore came as a surprise to many.