That's not really true. Genetics may contribute, but they certainly don't cause it. At it's core, obesity in the overwhelming majority of people is caused by a combination of eating too many calories, and not exercising enough (or doing the correct exercises; working out in zone 4/5 all the time isn't giving you the benefit you want).
I would challenge all people that are obese to have a metabolic assessment done to determine their true TDEE, and then eat at or below their TDEE while doing 1-2 hours of cardio (defined as zone 3 activity) + moderate weight training daily, and see where they end up.
As a former personal trainer, EVERY client i ever had was resistant to tracking their intake in any way. They flatly refused to even take a photo of every single thing that they consumed that wasn't water. They claimed to want to lose weight, but refused to do even the absolute bare minimum necessary to do it.