It’s important to remember that Kishimoto made and wrote and published tons of work without ever thinking through the backstory, so the Naruto worldbuilding is just a continuous process of attempting to retcon and stretch and gloss over and tie together a bunch of disparate puzzle pieces.
Not only did Kishimoto not originally think of Naruto’s nine-tailed fox as a being one of a set of tailed beasts, even by the time the Chuunin Exam arc had been written and published, he hadn’t come up with it. Gaara’s Shukaku was not originally supposed to be part of a set of nine tailed beasts with Naruto’s Kurama; they just both happened to have sealed demons. That’s why there’s that bizarre stuff about the monk in the tea kettle.
I’m not sure if Kishimoto just panicked or what, but he eventually started settling on “it’s fate” and “it’s prophecy” and “it’s destiny” to hold together a lot of the backstory of the main struggle of Naruto vs Sasuke. Naruto also became such a powerhouse success of a franchise that a sequel became a certainty, so Kishimoto couldn’t stick with the original true enemy of Naruto–the shinobi system–because actually fixing the shinobi system would eliminate the possibly of Lucrative Child Soldier Comic 2.
So in the Naruto ending, the ultimate source of everyone’s issues isn’t society or government, but aliens and fate. And the rabbit goddess is both.
You can look up on the Naruto wiki or similar if you want to know canon’s actual explanation for how the Sage of Six Paths (the rabbit goddess’s son) made the tailed beasts. You’re right, it’s weird, really weird, and more importantly, unsatisfying.
The tailed beasts as mighty forces of nature that got roped into humanity’s systemic power struggles are much more interesting than “Alien’s grandkids take inheritance struggle to world-ending levels of petty”.