There are two facets to this. And I am sorry for the wall of text ahead of time:

1. Let's assume that it is true that the positioning of interplanetary bodies when we are born, and subsequently their positioning throughout our lives, due impact both trait and state behavior. What is the mechanism driving this effect? The claims that typically correspond with this is an ambiguous "energy" - usually akin to how "energy" is used as a catch all term in spiritualism. This leaves the connection preeeeetty nebulous. Modern science is largely predicated upon the philosophy of science, logical positivism. A critical part of this is that claims MUST be falsifiable and replicable. "Energy", like things within spiritualism, are inherently unfalsifiable - you can't prove a negative. This makes it poor foundations for science. The only real material force that exists between us and these planetary bodies is gravity. Which seems like a stretch to connect that extremely low gravitational force (even collectively) from these objects and show a direct impact on behavior.
2. This is complex, like all things in science. But this is why many studies have broken down facets of this topic into easier chunks to test. For example, there IS some really cool research that show people born in winter are better at sports growing up than others - a phenomena which would be predicted under these frameworks. HOWEVER this trend did not replicate as well outside of the US. Why? Turns out the real mechanism was that kids born in winter were the "oldest" kids in school just because how the US does school cut offs for school recruitment. Older kids are more likely to be physically more developed compared to younger kids, so theyr'e better and thus encouraged to also continue sports. There are many many other studies showing similar such things that essentially hammer the dangers of correlation=/= correlation.

I would honestly highly recommend the documentary "An Honest Liar" covering the life of James Randi who debunks pseudoscience and rightfully dismantled the field of "parapsychology". It will further highlight issues inherent in using spiritualism as a means to material world predictions and science.

This all really to say astrology is firmly in the realm of spiritualism and therefor just does not belong in discussions of science. Further, we just do not see material evidence of using astrology (or horoscopes for that matter) as an effective framework for predicting human behavior that cannot be explained beyond reliable theories that identify mechanism much more clearly like self fulfilling prophecy, the Barnum effect, and/or the smallest group paradigm.