“Because it is the truth” — agreed. The very definition of God contains the basic obligation to serve Him without reductionism.

“And apparently there is also benefit for the Holy One, blessed be He” — do you really not see the infantilism here, in anthropomorphizing the concept of God? Does He need us? Are we helping Him? If He is so human-like, like us, then why is it a logical contradiction for Him to turn Himself into a mouse and for Puss in Boots to eat Him?

“And for the universe” — Kabbalah offers, as an alternative and contradictory explanation to an obligation toward God that does not need reduction, an answer to the idolatrous human psychological need to influence and build upper and lower worlds by waving lulavs while mumbling “for the sake of the unification.” I don’t understand how you believe these things, which have no indication whatsoever in the classical sources

If I saw it, I wouldn’t write it. He indeed does need us (I have written here more than once about service as a higher need), because otherwise there would be no reason for Him to create us. It is possible that I am infantilizing.
By force of logic. There is no other explanation for the halakhic system. But perhaps here too my infantilism is involved.

If God is not some sort of grandfather who one day decided to create a world, but rather something very undefined that perhaps can only be spoken of through negative attributes, it is better to say that we have no grasp at all of why He obligates us. I am surprised at you דווקא because I value you very, very highly and cannot understand this anthropomorphizing of God

I have answered this countless times. Maimonides’ invention of negative attributes really does not speak to me at all (there is a column about that). In any case, there is no anthropomorphizing here at all. It is a simple assumption about any entity of any kind: if it does something, it is for a reason or a purpose. Anyone who claims otherwise bears the burden of proof. Even in the Torah itself, He presents Himself as acting morally and toward a purpose.