It's because we're evolved for boom-bust cycles. Give it another 500,000 or so years and humans might evolve to cope with food always being available at all times.
Not only that, but type 2 diabetes makes you paradoxically more hungry - your body thinks it is starving because it cannot get sugar into its cells so it makes you MORE hungry which causes you to get heavier which often causes the diabetes to get worse which makes you MORE hungry which means you eat and get heavier and......
Not only that, but type 2 diabetes makes you paradoxically more hungry - your body thinks it is starving because it cannot get sugar into its cells so it makes you MORE hungry which causes you to get heavier which often causes the diabetes to get worse which makes you MORE hungry which means you eat and get heavier and......