Centrally controlled interest rates are basically price controls. The govt controls the price of money. Even a 5 year old knows price controls don't work, but we can't expect that from the govt.
A 400k house might instead be a 200k house, but you will never have 200k in cash compared to 20k for a down payment on a mortgage.
I manage a fund in Canada that does exactly that. We have a pool of investors, and lend out on mortgages only. Primarily in markets larger institutions won’t touch.
30-year fixed-rate mortgages for middle earners are a policy creation, not a natural market creature.
What rate would you feel comfortable loaning money to friends or colleagues at?
The question is more, how do you introduce money to the money supply (which you must do if for no other reason than physical wear/destruction of currency) without a central issuer who sets an interest rate on that issuance?