Vast majority being 90% according to IRS statistics. It seems it will take some time for the myth of the effects of the mortgage interest tax deductions to die down.
It is also capped at $750k of mortgage debt, which is not much for the 10% of filers who are itemizing and using the deduction.
If you are single it can definitely help. My deduction was 25k between SALT and the mortgage interest deduction vs 12,400 for the standard.
I wonder how the numbers look if you only look at Americans with mortgages though?