There are only a couple of mortgage wholesalers who fund loans.
Once these mortgage wholesalers close your loan, it will be sold into the secondary market, which include FNMAE, FRDMC or GIMAE, where big time investors will buy packages of mortgages to lower their risk.
These companies set criteria, credit and income requirements for loans they make based on current market conditions. We are at historic low rates.
Many factors go into this decision (underwriting) 
Credit & income will determine the interest rate you will pay.