Why does changing these registry keys not enable the screensaver?

Question

I'm trying to set up a powershell script that enables some screensaver group policy settings, so I found the corresponding registry keys and set them:

[HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Control Panel\Desktop]
"ScreenSaveActive"="1"
"ScreenSaverIsSecure"="1"
"SCRNSAVE.EXE"="scrnsave.scr"
"ScreenSaveTimeOut"="300"

All the screensaver settings appear to be correct; the wait time is 5 minutes and "display logon screen" is checked, but the screensaver never actually activates. When the settings are changed in the group policy manager it works fine.