Credit: Larus (Full Credits to Larus I didn't make this answer)
The correct answer is that it is too high for the weather balloons.
The mesosphere refers to the layer of the atmosphere of the Earth. It is present directly above the stratosphere and below the thermosphere. It elongates from about 50 to 85 kilometers above the Earth. The coldest temperatures in the atmosphere of the Earth, that is, around -90 degree C, is found close to the top of the layer.
It is tough to study mesosphere, therefore, less is known about the layer of the atmosphere in comparison to the other layers. It is tough as weather balloons cannot fly high enough to reach the mesosphere. The satellites orbit above the mesosphere, and cannot directly determine the traits of the layer.
