Is this so? The price of other assets going up doesn't change the riskiness of the bank's ability to repossess a home, in the chance the borrower becomes delinquent. You're borrowing money for a physical, durable thing in which the bank retains the deed until the debt is paid off. If the benchmark rate remains low, it's hard to imagine mortgage rates going up due to exogenous factors, or you would have expected us to see that in the past 50 years.

https://fred.stlouisfed.org/graph/?g=ITPc