Well, they don't all end their lives that way. But when a bug gets top heavy, it's in big trouble. That's because the bug usually falls over onto its back.
Of course, a stiff breeze or a curious pet can push it over, too. And once it finds itself belly up, it can be pretty tough for an insect to get back on its feet.
Bugs sometimes ock themselves upright. But if it's injured or it's weak or it's sick, it can have a really hard time. And even more so if a pesticide, or bug spray, is hurting its nervous system. That will cause a total system shutdown.