They can't. That's the point. They can't go to the G-league out of HS and get drafted until the following year anyway. So they're limited to at least one year at ~$35k and no chance at an NBA roster. Their option is to go to college and (obviously) get paid more than a G-league salary under the table with some benefits, or try and go overseas and deal with a whole rash of issues (e.g., very limited roster spots, lack of a support structure, sketchy contracts, language barrier, hazing, etc.). Just because there is some semblance of a choice, doesn't make it a real choice, nor does it allow for unfair treatment simply due to the system that is in place.