The equator receives equal day and night throughout the year because it does not tilt in relation to the sun's location. Because of the tilted axis of the Earth, the poles and locations away from the equator lean towards or away from the sun as an orbit is completed, while the equator stays in essentially the same location relative to the sun.
The Earth is tilted at approximately 23.5 degrees. This means that as the planet rotates around the sun, first one pole, then the other, leans closer to the sun. This lean is what produces the seasons, including the noticeable change in sunlight levels throughout the year. This phenomenon is directly proportional to the distance from the equator and most dramatic at the poles. However, throughout the entire orbit around the sun, the Earth's equator remains nearly the same distance away at all times. This results in an almost uniform balance of day and night throughout the year for locations closest to the equator.
Since the equator stays in the same place relative to the sun, the level of sunlight received throughout the year is nearly constant. The range of seasons common to locales above or below the equator are reduced to just two in the world's tropical regions. Instead of four distinct seasons, the tropics have only the rainy season and the dry season. The temperatures in the tropics tend to stay within a given range, although there are dramatic changes in weather patterns influenced by the warming and cooling of the rest of the planet. Even if the Earth had no tilt in its axis of rotation, the planet would still have an equator, which would still receive uniform sunlight throughout the year.