The Gemara says that eclipses happen because of specific Aveiros. The Maharal explains that the world, being created as a haven for such abominations, was created as a morally incomplete entity. Therefore, Hashem made its light accordingly, with flaws. It might have some astrological bearing, but it’s not born of an impact of Aveiros commited.
The rainbow is based on variables, which are manipulated by Hashem to reflect the current time. The eclipses, though, are preset and can be predicted in advance. If it were based on the current state of affairs, that would be a big breach of Bechira.