Why can't aerial photography be taken on many sunny days?

This question cannot be asked like that. Aerial photography must be sunny, but the altitude angle of the sun must be considered. If it is a mountainous area with a large elevation difference and a city with dense high-rise buildings, the sun altitude angle must be greater than 45° during Aerial photography, otherwise the shadow of the image is too large to meet the requirements of later data production.

Aerial photography field activities under favorable weather