Being around people who are smarter than you can be intimidating. Their presence makes you feel like a loser in the group. How uncomfortable.
Like most people, you then resort to surround yourself with others who are at least the same as or worse than you. This way, you can always feel like a winner.
Social proximity effect makes you mirror the habits of those you spend the most time with.
Would you rather be uncomfortable with being the loser in a group, but have the opportunity to adopt the discipline, healthy habit, and self-motivation of those smarter than you? Or feel distinguished, but risk adopting the procrastination habit, binge-eating routine, and sedentary lifestyle of those lesser than you?
