Most of what you can buy in a grocerie store is bad for you. It has been optimized for profit, i.e. consumption.

Then you can of course pile on all kinds of contributing factors but this isn't necessary to understand why people are fat.

I don't blame fat people for being fat but it's not a mystery why they're fat. And it's not easy for them to change everything about their lifestyle to get fit but that's what they need to do.