I think the average for a student taking all 4 years of loans is $29-30k, which would be the $27k in actual principal borrowed plus interest accrued on the unsubbed part ($2000 per year minimum).
Why $5500? That’s just what the limit was set at when the limits were set. Might be more than enough at a CC and not nearly enough at a private school. It is a ‘one size fits all’ plan when clearly it fits very few.