They're not obliged to. Conservation is a good on its own terms. They also didn't address carbon burdens, asbestos or diversity.
Look I get it, there's a housing crisis. If you want to argue we should make suburban Seoul with towers for 10km can I remind you le Corbusiers ideas were implemented widely in Birmingham and Manchester and were a disaster.
Maybe, the answer is to raid the green belt? Oh look, another "special interest" bun fight. More Barrett homes now! More ticky tacky. More all the same.