How does reason relate to insects, in particular social insects like ants, bees, and termites?
Most of the animal biomass on the planet consists of tiny unreasoning worker and drone insects. Their survival seems strictly based on the fecundity of a relative few organisms, not any sort of brain-power.
The short answer is that the insect survival strategy took a different path. The ability to reason isn’t the only survival characteristic, just *a* survival characteristic. Evolution is really the sum of a wide array of factors interacting with each other over time, and a tiny change in any one of those factors can produce profoundly different results over a long stretch of time. Some animals survived because they produced a huge number of offspring so at least some would survive, while others survived because they invested more energy in a small number of offspring.