I suppose I can only speak for myself:
My obesity was 100% my doing.
I ate in excess, and I was sedentary. It wasn't my genetics. It wasn't some disease. It wasn't my metabolism. It wasn't an injury. Sure it's take a lot of hard work to get all that weight off, but there was NOTHING standing in my way except ME! Unless you count excuses and laziness as "not my fault", but I don't think either of those qualify as such.