>What am I missing?
>
>Rent is $2500 and monthly expenses are ~$2600.

Nothing, you answered it right there. People pay off that much debt quickly by continuing to live the "poor grad/medical/law student" lifestyle they're accustomed to for an extra few years, and plowing everything towards their debt. It's easy to pay off $300k+ in loans if you take home $15k/month and live in a $1,000/month apartment, drive a paid off car, and eat cheap home cooked meals.