We’re not. We’re taxing the income you receive from providing that roof to the occupants each year.
If you are an owner-occupier you just happen to be the occupant as well as the landlord. That is no reason for tax not to be paid on the transaction.
The benefit you receive each year from owning the house is every bit as real that you receive from owning a bank deposit or from rent paid by a tenant. Why should you be tax exempt when tenants have to pay rent from their income
after tax and their landlord pay tax on that income received?