I think it has to do with desk jobs/sedentary life-style. I believe that before machines/computers came along an average person burned in excess of 3k calories/

I think it has to do with desk jobs/sedentary life-style. I believe that before machines/computers came along an average person burned in excess of 3k calories/day toiling in the field or doing some other physical job. Now I would be surprised if the average person burns more than 2k calories/day. Moreover, once you get to high fat levels your body produces more estrogen like hormones. These indirectly lower your metabolism even further. This is because those hormones impede the synthesis of testosterone, which is highly correlated with muscle-synthesis and muscle fibers are much more metabolic active tissues than fat. A feedback loop that is really hard to escape from.