Construction costs don't scale linearly with rent prices, it's a different market altogether that depends on regulation/worker supply/material costs/equipment/etc.
As long as construction costs remain below the value of the units all-in, there's profit motive for developers to build.
> As long as construction costs remain below the value of the units all-in, there's profit motive for developers to build.
Not true
Real estate development is extremely capital intensive and therefore it's a question of all-in cost of capital compared to other investment opportunities.