Even if you have all the money in the world, US high school standards are very low. With some affinity for reading and access to the internet, one can be learning at a far quicker rate, even without sacrificing social life outside of school.

Many kids in the US already do this via Advanced Placement testing, but some states also allow high school students to take college courses.

1. You want or need to be making money instead of spending it.

Eg, no family wealth involved; you’re paying for everything yourself

2. You don’t enjoy the high pressure (ish), test-driven environment and want to be doing more meaningful work.

Etc. The number of people who don’t want to spend money and time in college might surprise you. I even know some very academically successful ones with this attitude.