Why dont we get hungry in hot summer season?

It depends if your hungry or not most people loves to eat in a picnic outside or some people likes to eat in the house in summer days because its super hot and they need to stay cool and hydrated.

I would say that's it's not really linked with it being hot outside, but just that during the summer, more people are out doing things. And when it's colder, most people are likely to stay inside. When you're inside you tend to eat more, because you aren't as busy and it's more convenient. Some studies say that is has to do with light sensitivity.