Okay...you just missed Ch12's entire point. First, with "assigned seating", a lot of people in row 20 will toss their bag in the bin for row 12 so they can "grab it" on the way off the plane. When row 12 is called, there isn't any space in the bin, so those folks have to wander around the plane to find an open bin space, then get back to their seat. There is no advantage for someone doing this on Southwest - you put your bag in the bin over your seat, then sit down. Someone in boarding group C is most likely to find space in the overhead pretty near the seat they sit down in. But even if some idiot does this on SWA, someone right behind him may just grab the seat in row 12 - because they weren't putting anything in the overhead bin - and when a "latecomer" gets on board, the only available seats are in the back of the plane anyhow.
"A lot" of people? Sure, I've seen a few people have to go hunting for bin space, but you two are blowing it way out of proportion.
Besides, what is someone to do on Southwest who boards late where overhead space is here, and the only empty seats left are over there? Same thing; you get to drag your suitcase around. It's not the end of the world, is it?
Secondly...it's easier to say that Southwest doesn't need more passengers who pay higher fares because Southwest is making a profit on the passengers they are carrying. Their relatively low load factors are somewhat misleading...it's easy to do when you have upwards of 20 daily departures in some city pairs. Some of those flights will be chock full. Some will be half full. The result is a system wide load factor of 75%. It's called "frequency". They are able to make half full flights work because there are already several completely full flights on many routes that day.
So Southwest is not interesting in increasing their profits? What an odd business strategy:
We make enough money as it is. We're not interesting in making even more money.
Send some of the extra, unwanted money my way -- I'll put it to good use!