Parental neglect. Parents replace time spent parenting with time spent feeding because said parents are lazy as fuck and don't want to put in the effort required raising a child. Similar issue placating children with a display screen, be that a tablet/phone or letting that TV raise them.

Sure these things being a modern facet of the world are important to have some experience with as both social and work interactions can rely on them, however fully shifting the responsibility from parent to object will cause problems like the pic above. Simply because the parents involved are shit for various reasons.

Abuse. Parents are overfeeding her for one, but maybe she was also victimized in another way and turned to food to cope. Maybe a broken home, depression. You see this on 600lb Life, these people have sad childhoods and are often fat even at 2, 4, 6 years old.