For the record, the interest rates on federal loans are set by Congress, as are the annual and total limits for each type of loan that a student can borrow. The interest rate and limits on private loans are essentially set by the market in the same way as other loans. The government wanted Sallie Mae and other lenders to lend a limited amount of money at low(-ish, I would't call the 6.8% I have exactly low, but its certainly better than some private loans) rates, and they do that.
The fact that federal loans no longer cover 100% of tuition and expenses at a growing number of universities is a symptom of a larger problem that extends well beyond Sallie Mae and their high private loan rates. Honestly, I don't think most people are in any position to pay back more than the max federal loan amount when they graduate and still be able to buy a home, start a family and do the other things people want to do (like start a business, invest, plan for retirement). Your anger is probably better placed on the issue of the cost of schooling, than the cost of borrowing way more money than most people should in the first place.