> deflects the question one level down without explaining anything

There’s a lot of levels to SOC. Which do you think is “because it is?”

If you’re asking why spin values are restricted, it’s in the spin-statistics theorem [1]. If you’re asking why spin causes charge, that’s SOC. There are lifetimes of understanding contained within those layers.

[1] https://en.m.wikipedia.org/wiki/Spin–statistics_theorem

The question wasn't "why do protons have +1 charge", it was "why do protons have +1 charge, *considering electrons have -1 charge". The fact that possible charges are restricted to a few values is a much more satisfying answer to the latter than the former

Physics doesn't attempt to answer the question "why", it answers "how".

Richard Feynman addresses a similar "why" question in a great way in this interview[1], and how "why" questions are problematic in science.

[1]: https://www.youtube.com/watch?v=36GT2zI8lVA

You eventually have to take _something_ as given.