One of the major causes of being overweight in adults is being unable to exercise due to physical limitations. Another factor is depression. Often those 2 factors go hand in hand in the development of an overweight person.
When an adult becomes disabled they often go on social security disability. If their disability is not apparent to the average observer then they could be the victim of ridicule. That ridicule will often cause the disabled person to become depressed and that depression can lead to overeating, alcoholism or even drug addiction.
Contrary to popular belief, being on disability is not a free ride but only enough of an income to barely get by. Next time you see an overweight disabled person consider that over eating might be their "mental crutch" that they have had to lean on due to depression.