The mortgage tax deduction was not introduced in the 1980’s.
All interest (mortgage, credit card, etc) was deductible prior to the tax reform act of 1986. At that point most forms of interest were no longer tax deductible. Exceptions were made for mortgage interest with limitations (maximum value of loan limited to 1 million and up to 100K of home equity lines). Mortgage interest has been deductible since at least 1913.
