Because in the (fairly wrong headed) world of today, the developer is told what to do by product folks and they mostly do it.
That alone gets you to situations where the devs can see it obviously won't work, but the incentives and the egos are setup so that your job is just to build it, not critique it.
That alone gets you to situations where the devs can see it obviously won't work, but the incentives and the egos are setup so that your job is just to build it, not critique it.