There is a genetic aspect I'm sure. But I think most people don't avoid consequences of, say, drinking lots of soda while not brushing teeth. I bet there are nutritional factors too. If you are chronically malnourished, your teeth may be worse somehow.

I think regularly brushing your teeth and getting cleanings makes a big difference obviously. Gum disease or gingivitis mainly happens to people who have long-term dental care issues or certain bad habits.