What's the role of the detailed descriptions of the other planes of existence? Why it was important for the Buddha to tell them? There are many repetitions of categorization of the different worlds in the Pali Canon that make me a bit confused.

I'm not trying to rationalize them as metaphorical or as a "later addition to the scriptures". I am also not searching for a confirmation. The universe is probably endless and we percept only a tiny fraction of waves coming to our ape senses. There could be myriads of other planes and beings that are present but undetectable with any human-made tools and observable only by an enlightened mind.

But why did he even bother to start on this topic? He wisely answered with Noble Silence to other existential questions that could bring additional disputes and disagreements (like the Buddhist cosmology does today in "Buddhism vs. Scientific Worldview" debate despite scientists allow themselves to make up concepts like "Boltzmann brain" or "multiverse" without any issues).

And then there is this strict distinction between these worlds although they are not even "real realms" but a flow of dependently originated events. Like we're saying "human world" and "animal world" but in the modern eyes they are not even separate.

So what am I missing? Why the Buddha couldn't reduce it to "bad karma leads to hellish worlds, good karma leads to heavenly worlds" but went for this detailed naming and descriptions of beings, deities living there?
Mr Ivan ("god is merciful"), because the Buddha did not like Mr Ivan to mistake an realm of existence for Nibbana, or the heartwood. That is why he described those states of being in detail. So when you start to travel, and do not just ponder why you should not travel yet, Mr Ivan is well prepared.

In which plane of existence did you now take place? Nobody aside of Mr Ivan would know that, does Mr. Ivan do?

(Note: this answer has not been given with the agreement to be means of trade or the purpose of/for trade and/or keep people trapped and bound. How you handle it lies in your sphere, but does not excuse the deed here either.)