Why spouses credit score?

[jimmy]

I have applied for a FHA loan reporting only my income which is more than plenty as means of repaying the loan. My score is in the 660s, no bad credit, I pre-qualified at the bank within FHA guidelines. A realtor prepared the home sellers / buyer contract which I presented to the bank. Now the bank says my wife’s credit score must be looked at and they (FHA) will use the lowest score. My wife has no score or credit.
Why must they have her score when loan repayment is based solely on my income?
Thanks in advance, Jimmy in Texas