Not being double-blind makes it cheaper. Hence takes less budget, lower taxes, everybody cheers. Anybody proposing to make it double-blind is going to need to

Not being double-blind makes it cheaper. Hence takes less budget, lower taxes, everybody cheers. Anybody proposing to make it double-blind is going to need to find the money, either from other departments or by raising taxes. Without a chorus of public support behind them, this is a very hard sell. And easily reversed after the next election.