Why can't I lock my computer and have Windows turn off my displayport monitor without having it turn itself on and off every few minutes until I log back in?

Why can't I turn off the power button on my monitor and then turn it back on to keep using it again without having to shut down my PC, turn off the PSU switch, press the power button to fully power it down, then bring everything back up? I just want my monitors off when I'm in bed...