Why do people live in flood areas, and are NOT prepared for floods?

It hurts to hear about places like memphis flooding and not think about precaution in my own life. no place is 100% percent safe. there is always some type of natural or man made disaster. BUT I do not undersatand why people are not prepared for the ones that are most likely to occur where they live. so what if katrina victims can't swim, are you telling me no one had a $1 to buy some cheap kid's swimming floaties? i find that hard to believe if you have $100 sneakers on. If cleveland requested national guards because they were covered in a foot of snow and had no shovels, snow plows available people would say wtf you idiots thought you wouldnt get snow in january! i live in a crappy snow town and although i barely have a pot to piss in, i at least have a cheap shovel, salt, and ice srapper. that is all i'm saying, i'm not suggesting everyone have a million dollar plan but come on, when i see perfectly healthy teens and young adults scrapping for their lives all i can do is say....... &^$%^(*)*)*%^$%$%%$&*&(*)....... nevermind.... come on not even a water noodle? a doughnut?