Why?
People with substantial amounts of crypto would like to be able to finance larger purchases directly in crypto without needing to liquidate into fiat first
Buying property with ill-gotten gains is an extremely common method of money laundering. Having a large hoard of cryptocurrency that you prefer not to liquidate screams "I'm trying to pretend that this isn't a taxable event."
We don't let people pay their mortgages with pre-tax stock gains, why the fuck are we bending over backwards to let people pay their mortgage with cryptocurrency?