Food addiction is a thing
But most people eat when they're bored
Or they are emotional eaters
Lots of people snack and don't realize they are snacking
Other people think they're eating healthy things but misinterpret what's on the packaging. Like tic-tacs being labeled as sugar free even though they're 100% sugar candies, they just weight less than a gram and one serving of a piece of candy on it's own is harmless but if you eat a whole box of them then you're going to put on weight from all of the sugar.
There are the people who grew up in homes with poor eating habits and were just never taught what foods were healthy or how to control your diet and eating habits and portion sizes.
Poverty has a huge impact on weight, cheaper foods are calorie dense. Fast food is readily available in areas that don't have fresh food markets.

And still...the moment you see a fat roll, you get a pot belly, or when you can't fit into your favorite jeans should be the wake up call for most people, to diet, and exercise, but they don't care, they just keep eating, so my sympathy is rather limited.