I don't know your background but I've talked about music theory with a lot of non-musicians who tend to have the same complaints. A lot of what you describe I learned when I was like 5. I don't really think about it anymore, it is second nature on any instrument I play. Even if I don't know the instrument, if you show me how the notes work I can play any scale without really putting any thought into it. This is supposed to be a college level text book. Likely, if you have to think that much about how a major scale works you probably don't have an adequate background to study this. It's not that someone can't but it'll obviously be more work.

These sort of traditional music courses are designed around understanding western classical music. There are some scientific reasons for the way things are but they weren't developed by scientists. This sort of music theory will 100% help build an intuition into western, mostly classical but not exclusively classical, music.

If you want to know why the major scale is the way it is, go take math classes, a few physics courses will likely help as well, probably by the time you're in graduate school you'll understand it and can explain it better than 99% of musician. It'll help you in no way in creating music.

Essentially, what these complaints boil down to would be something similar to someone trying to learn to drive by first learning how an entire car works. It might be interesting to some, but it isn't the point.