Lazy staff or conspiracy underhand?

Originally from

No photos, I'm afraid, but considering a short discussion earlier as we passed through the open barriers at Central station - Is this a conspiracy, or just a matter of lazy station staff?

It is something of a fact that around 10:00PM, sometimes earlier, and sometimes a bit later, all the ticket barriers at Central station will be open and free for commuters to pass through without inserting a ticket - you can try, but it won't be accepted into the machine anyway.

So the question is, is this because station staff are rocking off early (or I assume early, I wouldn't really know about station staff hours) and can't be bothered manning these ticket barriers any longer, or because this is a conspiracy to earn money of fare-evading commuters?

Surely those open gates are just inviting (often teenage) commuters to decide a ticket is not necessary?