I find it depends on the length of flight. On shorter flights there aren't that many people going to the loo so it feels kind of unnecessary to police it.

On longer flights, a significant proportion of the passengers will be going to the loo, queuing etc, and this becomes a problem in CE.

None of which would be an issue if the cabin crew had curtain-closing as a mandatory part of their procedures (I assume it's on an entirely discretionary basis at the moment?).