The confusion here is between dual degree and dual major, they are very different. A dual major is when you are in an academic school, and you get bachelors in two different areas (like a bs in computer science and a ba in history). A dual degree usually refers, in the music context, to getting a BM (performance degree) from the music school and BA/BS from the academic side. The reason it is dual degree is because the BM track is very, very different from a BA track on the academic side, whereas if you get two ba’s let’s say, much is common between the two, some of the requirements might be the same for both tracks so you can save time, etc.
One of the things to be careful about is what a music degree is. Keep in mind that music major can also mean someone majoring in composition, music theory, music history,ethnomusic, etc, it isn’t necessarily a performance degree. Many schools offer degrees in those kind of subjects, but don’t offer a BM at all, some programs you can get a BA on an instrument.
It is very difficult to do a BM dual degree program, it is doable, but difficult, because the BM is pretty intense. Bard college conservatory forces its kids to do a dual degree, and the program is 5 years (many dual degree kids take that long). Other kids go to the elite universities (like the Ivies) that don’t have BM degrees but have strong music programs and actively recruit strong musicians to fill out their orchestra and ensembles (they also often pay for lessons as part of your tuition), kids will do that kind of music, get a degree in something, and then go on for an MM…
I know it isn’t easy, but if you look through the threads on here, do a search on ‘dual degree’, for example, you will see a lot, this has been discussed a lot over the past X years I have been on here.