Bus Logic: If There Are Twelve People Standing in the Aisle and Eight People Leave an Open Seat Upon Their Departure, How Many of Those Still Standing Will Notice?

It is 20 degrees outside, dark by 5:00 in the week before Christmas; and the bus patrons are packed in tightly, pressed against each other like sweaty, down-insulated sardines. 
In the event that the bus crashes, this is the kind of thing that will work in our favor:  no one will be hurt, we will simply be mashed into each other, forming one enormous commuter. 
Bus Crash on the Number 17 Leaves 36 Permanently Fused.  “It’s not necessarily a bad thing,” says Head #8.  “Showers are more difficult; but as part of one large commuter, my daily bus fare is literally pennies.”
Me, though, I am one of the lucky ones this time around; one of the cake-eaters that have nabbed an actual seat.  Rather than being compressed between people carrying shopping bags and, from the smell of it, curry, I have only my seatmate to deal with, a pleasant-looking man who takes up no more of his half of the seat than he should. 
This is how rich people travel.
In the aisles, though, the masses sway as the bus lurches down the line, toward home, toward work, toward the immediate future. 
And as a bus will do, the doors open and people get on.
At the same time, people get off. 
Oddly, while the people at the back of the bus exit through the rear door, the people standing in the aisle near the front fail to turn around, fail to notice, even as others get on, that there are now empty seats and instead remain packed tightly against each other.
I lean into the aisle.
“Excuse me,” I say toward a heavily backpacked young man’s backside. “There are seats back here.”
Backpack doesn’t turn around.  Further inspection on my part reveals a thin cord running up the neck of his jacket.
IPod. 
He can hear nothing.
And because this person isn’t moving back, no one will move back.  They will remain crammed together, at the awkward whim of gravity and traffic conditions.
This sort of thing makes my head buzz. 
I turn to the man seated next to me.  “Why doesn’t anyone turn around?  When more people get on the bus, why doesn’t someone turn around and see if there are seats?”
He smiles at me.  “Baaaaaaa,” is all he says before he goes back to staring out the window.
I close my eyes.  I am no shepherd.
And the Number 17 travels on.