The answer is, it isn’t. There are many factors that are considered in the loan approval process and income is not necessarily the most important.
These factors include but are not limited to:
The Loan amount as compared to the value of your home purchase.
The length of time on your job.
The type of property you are buying.
The use of the property once it is purchased.
Your assets and reserves. Typically, bank accounts, retirement funds, life insurance, stocks, bonds, and similar assets.
Understand that credit is not just measured by credit score. Some loans, for example, FHA, do not use credit score as an underwriting guideline.
Credit scores and the type of credit model you have are sometimes used in conjunction to measure your willingness and ability to pay for the mortgage you have applied for.