Homes appreciate in value, whereas RVs depreciate. Home is a much safer loan for the bank.

Your initial salary may not have been great, but you just graduated with an advanced degree into a "safe" field with a good opportunity for higher income later.

Student debt is also treated much differently (and generally has lower monhtly payments over a longer period of time, so not an outsized effect on DTI)

For calculating DTI, usually only the minimum payments are calculated for the consumer debt. Not always the best metric.