Renters are overwhelmingly living in properties that have mortgages against them and commercial loans are always deductible. The deduction for mortgages on owner-occupied property serves to put prospective owners (including current renters) on a more equal footing when bidding against landlords for property.
It is an immense giveway to the top income quintiles, which receive between 70-80% of the benefit, and giving "prospective owners" preference over "landlords" practically by definition reduces density and thus affordability.
Again, that is inherently a policy decision that reduces density and affordability; by definition, "landlords" are people that own and operate multi-family dwellings. You could just as easily ask "why not give more of a preference to landlords?"
It's probably useful for you to understand my, uh, priors? about this, which include the fact that I live in an overwhelmingly SFZ community that actively works to prevent the construction of multi-family dwellings, often with appeals to the evil of "landlords".
I'd prefer that an owner-occupant be able to write off the interest on N/N units on a parcel, just the same as a landlord is able to write off the interest on N/N units.
That's true for N=1 (SFR), N=2 (duplex, half-occupied by the owner), N=3 (triple-decker with owner living in one), or N=50.
