cg, imagine disembarking 300+ passengers in to the terminal. They will wander off despite being asked not to. Toilets, food, shops etc..
Now you get the go, slot in 20 minutes, if you miss it it'll be another 10 hours before you get another chance.
Can we have our passengers back please? Most of them you can, we've lost a few. Bugger, better get their bags off then, they won't be happy. Can't find the bags or the passengers in time. Slot missed. Another 10 hour wait. Oh and we need the stand so we need to reposition you to a remote one miles away.
That's one reason, don't know about this particular occasion though.