The pressure difference between the equator and the poles is primarily caused by the amount of heat in each area.
At the equator, the sun's rays hit the Earth more directly, leading to higher temperatures and, consequently, lower atmospheric pressure. In contrast, the poles receive sunlight at a much lower angle, which results in cooler temperatures and higher atmospheric pressure. This differential heating creates a pressure gradient, which drives atmospheric circulation patterns, including the trade winds and other wind systems.
While factors like the rotation of the Earth (Coriolis effect) do influence wind patterns, the fundamental cause of the pressure difference itself is the variation in heat received at different latitudes.