Own your shitty lifestyle. I make poor health choices all the time. It's bad for me and it makes me feel bad about myself. But it's on me. Nobody forced me. I acknowledge and own the decisions.
Using a lack of a "walkable city" as an excuse is pathetic. You can exercise in a tiny room if needed. You can drive to a gym. Or just to a park. Or to a national park. At work you can take the stairs. I live in a country 15 times denser than the US so don't tell me you don't have space to move around.
What would be your next excuse if you would have a walkable city? Obesity is OK because Twitter said so?
There's no excuse for your crap diet and inactive lifestyle. Is it impossibly hard to change? Yes, I totally feel that. But start by owning it.