There are of course advantages to having the gate security. I've arrived at HKG slightly late, leaving just 40 mins to transit and already proactively moved to a flight 3 hrs later, likewise my partners mother arrived 45 mins before onward departure and got moved to a flight 8 hrs later. Whilst at SIN, last time I flew in we were 40 mins late, leaving only 20 mins for LHR bound pax, but staff were directing them all to the gate (2 gates over), which usually close 10 mins before departure. It looked like they were all going to make their connection, something that would difficult with central security, and the other upside for some travellers (such as Solitaire and First pax on SQ, or those who are departing on a later flight, but have a long transit and wish to go into Singapore after eating and freshening up), is lounge access on arrival.

It also stops passengers pilfering drinks from the lounges for their flights .