The Apterygota were the first insects to evolve. The evolution of wings took a long time. Why do some vertebrates (e.g., birds, mammals, reptiles) have legs whereas others (e.g., fish) don't? Same answer. Legless vertebrates were the first to evolve, and the evolution of legs took a long time. And yet, wingless insects and fish are still with us.
Flightlessness is a separate issue. Many insects that lack wings or have reduced wings are descended from insects with wings. Queen ants and queen termites shed their wings when they go underground to start a new colony. Who needs wings underground?
Wings evolved early in the history of insects, but some insects have evolved to have lost their wings. Flight is undoubtedly useful but it does have its costs. It takes a lot of energy to fly, so if there is not the need to fly, then an insect can save a lot of energy by not flying. For example, most individuals inside a colony of ants and termites are wingless. By not flying, the ants and termites save a lot of energy because the worker ants eat a lot less if they don't fly.
Flight also imposes limits on how heavy or big an insect can be. By getting rid of flight, an insect can grow much larger. Larger animals generally win flights more easily. For example if two dung beetles are fighting over a piece of dung, the larger one usually wins. Since dung contains everything a dung beetle needs, it does not need to fly to find other sources of food.
why do some have wings but others dont? Whats the purpose of no wings?
