Because the temperature is different
The heat absorbed is different.
When sunlight hits one side of the tower, it will expand slightly.
So it will tilt a little to the other side. This is a very subtle phenomenon that happens every day.
Growing taller and getting shorter is a seasonal relationship.
Steel materials can receive different heat in different seasons.
So the degree of expansion is different.
The height difference between spring and autumn is about ten centimeters.
But it's all changed a little.
Will not pose a safety hazard to the tower.