Why is the equator so hot?

Because it is near the sun.

Second answer

The earth is an oblate spheroid, meaning that it is wider side to side than it is tall top to bottom--i.e., it is not a perfect sphere. This means that the equator sticks out the furthest and is exposed to greater amounts of sun.

Third answer

As we all know that equator is the imaginary line which divides earth into two hemisphere, northern hemisphere and Southern Hemisphere. The sun rays fall directly on the equator as a reason it stays hot the whole year.