why is it cooler in regions further away from the equator

because places away from the equator get slanting sunlight and the sunlight spreads over a larger area than vertical rays, so same amount of  sunlight is spread over a larger area. thus, places away from the equator remain cool

because sunrays cannot reach directly on the region away from the equator and sunrays directly fall on the equator.

Because sun rays fall vertically on equator and they fall obliquely on the places away from equator. Oblique rays provide less solar energy that is Heat to the places.

because on 30degree it is cool and hot air is then replaced by the cool one and then the cycle is managed an there is one more way which is that the sun is giving its maximum heat to the equator.