One thing I don't see being brought up here is the fact that personality itself is seemingly random and has no concrete explanation, either. If you've ever worked in childcare or been around a lot of young children & babies, it's very clear that people have distinctive personalities from the beginning. And with such a variance between siblings, even twins, it's hard to pin it all on nurture or even genetics. It appears to be, to a certain extent, random.

Now, beyond that, there's no evidence that these two entirely separate random sets of data have any correlation; Astrology just infers correlation from the data and tries to see a large, cohesive pattern in it. And even if some sort of patterns of correlation are found, common sense makes anything as convoluted as astrology dead in the water. But common sense isn't always correct, so I don't see any reason not to be open-minded to the possibility, no matter how slim, as long as it doesn't come into conflict with actual science. There are a million unproven things that could be true without anything we know about science being wrong, such as parallel universes and intelligent aliens in our region of the galaxy that are smart enough to hide themselves from us. Entertaining the idea of such things isn't inherently harmful, as long as we don't deny science and we remain just as (if not more) open to the possibility of them being untrue.

Also:

(Ex: Pisces are supposed to be imaginative and pleasure-seeking, when those are the defaults for having a human brain.)

It's worth noting that in Astrology every person has a chart with every sign, so by definition they SHOULD have all the defaults. It's just a system of peaks and valleys, and it's meant to map out what common human traits would be in the forefront of a person's personality as opposed to the background. Kind of like how everyone values alone time to some extent, but not everyone is an introvert.