This is a fair point. In honesty I think the intention behind building codes is to prevent builders from building buildings that endanger others (e.g., fire hazard) or selling buildings where the buyer is not aware of the risks. The former I think we can all agree is necessary and fairly straightforward. I think the latter is more complicated. Perhaps people can't effectively judge the risk they take on by living in a potentially less safe environment and so are not willing to pay for improvements that would improve their utility?

Selling houses is a very formalized process, this should be easy to enforce. First of all, there is a deed of sale that gets signed over, the unsuitability for resale could be listed on the deed. Remember selling a house usually is a super involved process that costs 10s of thousands of dollars.

It almost sounds to me like you don't WANT to find a better solution.

It's true. I don't think it's a good idea to have a class of houses that conforms with code and another that doesn't.