Seasons are primarily caused by the tilt of the Earth's axis, rather than the shape of its orbit. The Earth's axis is tilted at an angle of about 23.5 degrees relative to its orbit around the Sun. This tilt is responsible for the varying lengths of daylight and the changing angle at which sunlight strikes different parts of the Earth throughout the year.
When the Northern Hemisphere is tilted towards the Sun, it experiences summer because sunlight is more concentrated over a smaller area, resulting in longer days and more direct sunlight. Conversely, when the Northern Hemisphere is tilted away from the Sun, it experiences winter because sunlight is spread over a larger area, leading to shorter days and less direct sunlight.
At the equator, the tilt of the Earth's axis has a minimal effect on the length of daylight and the angle at which sunlight strikes. This is because the equator is the closest point on Earth to the Sun's path and is always near the center of the Sun's rays throughout the year. As a result, the equator receives fairly consistent amounts of sunlight and experiences little variation in seasons.
While the Earth's elliptical orbit does affect the distance between the Earth and the Sun, this variation in distance is relatively small compared to the impact of the axial tilt. The elliptical orbit does lead to slight variations in the intensity of sunlight received on Earth, but these differences are not significant enough to cause distinct seasons at the equator.
In summary, the lack of significant seasonal variations at the equator is primarily due to its proximity to the center of the Sun's rays throughout the year, which minimizes the effect of the Earth's axial tilt.