In addition, airside is actually more convenient for T3/G connecting passengers in SFO who are already airside but never landside. So airside has other benefits beyond those you note.
But seriously, you're absolutely right. Indeed, connecting passengers might be using this lounge about as much as us locals and those visiting here. Those connecting to Asia, Australia, NZ and Hawaii usually need to be on the safe side in giving themselves a time gap between scheduled arrival and departure times. If they miss the connecting flight, they might be stuck at SFO for a day or more.
If such connecting passengers arrive roughly on-time, they'll have some time to kill at SFO. This lounge would be great for that. Airside T3 means airside access to about 40% of the gates, but I'm guessing a majority of the connections -- and nearly all of the long-haul connections.