Because then they might as well just turn it into a coupon for everybody to use. Anybody could just say "Hey I'm self-taught!" The whole point IS to give a discount to people enrolled in school and spending a lot of money already.
As for paying full-price, if you're in the US, I'd suggest looking at places like Audiodeluxe who usually have very good prices for VSL products. Also the products are more than worth the investment!