3. Being on a hillside during a severe flooding event can be a disaster, as your home begins moving downhill with the water.
4. People on hills still need roads.  Flooding can leave you isolated in your home, with no way to get out.
5. People on hills still need the grid, and running water.  Those things can be undermined by severe flooding.  Is all the infrastructure on hills?  Do all the repair people live on hills?
6. People on hills have friends, family and loved ones who do not live on hills.  Watching your neighbors drowning or standing on their roofs is not fun.
8. Most downtowns are...well, down on the flatlands of most towns (not all) which means the local businesses you rely on may not be open.  Do you need groceries?  Medications?  Banking?  Schools?  Hospitals?  Do you care about your local economy?  The people most likely to be driven out of business are the small business owners and farmers who can't afford to lose everything...