I forgot the details. It's not a blanket requirement but has to do with FEMA money. Basically, they don't want people relying on FEMA instead of buying insurance.
"If you receive disaster relief funds following a disaster declared by the president, that money often comes with a caveat that you buy flood insurance to cover the cost of repairs or a replacement building if it is in a high-risk area for flooding. The Federal Emergency Management Agency requires that you maintain flood insurance on the property for as long as you own it. You’re also required to notify the next owner of the requirement if you sell the property. If you fail to cover your home with flood insurance after you receive federal disaster aid, you’re ineligible to receive future relief."
"If you receive disaster relief funds following a disaster declared by the president, that money often comes with a caveat that you buy flood insurance to cover the cost of repairs or a replacement building if it is in a high-risk area for flooding. The Federal Emergency Management Agency requires that you maintain flood insurance on the property for as long as you own it. You’re also required to notify the next owner of the requirement if you sell the property. If you fail to cover your home with flood insurance after you receive federal disaster aid, you’re ineligible to receive future relief."