It's clearly because it doesn't have enough sun. But there are plenty of other factors that could explain it.
The sun has an energy range (about 10,900 watts per square inch, or 11.2 megawatts) with all of Earth's surface covered by the planet's atmosphere, leaving little or no sunlit soil at ground level, allowing solar radiation to escape the atmosphere at speeds up to 6,300 miles per hour ("the speed of light") and onto Earth's surface.
Solar radiation can break up more readily into smaller particles which then enter the atmosphere. This leads to some changes the climate and precipitation, and a larger increase in evapotranspiration, an increase in surface temperature, and less runoff, which slows water evaporation and makes water more quickly absorbed by plants.
The effect of this on climate is a complex question, but climate models are a useful tool that give estimates of the current climate. As the climate has changed, temperature has varied, too, and solar panels with a shorter distance from land can reflect more sunlight and absorb more heat.