It's not just the abundance of food, it's the sustained abundance. Many species follow a feast / famine cycle which puts pressure on stocking up as fast as possible during feast in order to survive the inevitable famine. This is the evolved instinctual mechanism which gets shot to piece by the "endless feast" available to many individuals in advanced economies (or wealthy enough individuals in pre-industrial economies), even more so combined with the physical "leisure" (limited requirements of extensive physical activity in day to day life).

But some seem fine with layers of blubber. It's a feature, not a bug sometimes.