A lot of instant gratification and brain short-circut building. I agree, it's extremely difficult to get rid of these things.
BTW do you know that approximately only a third of people has positive healthy food related habits?

https://steemit.com/health/@katenok/economic-graph-of-the-day-4-how-healthy-are-your-habits
RE: Why Do We Have Bad Habits When We Know They Are Bad?