Ah they do? I was flying Southwest a few years ago (right before COVID) from Phoenix to Oakland (via Portland....) and the seats were assigned. I remember this because the whole family was scattered around the plane despite us coming in rather early and all together.
You must be misremembering. Southwest has an assigned boarding order, and you pick any seat when you board. It is likely that your family was scattered around because of limited available seats when you boarded. Those who fly don't fly Southwest very often aren't familiar with the check-in process and often end up in the later boarding groups. Showing up and checking in for the flight in-person typically results in a late boarding group, because most of the good boarding groups are already taken 24 hours before the flight when online check-in opens up.
This is probably due to the weirdness of that flight. It was our last day in the US and we were to fly from PHX to ODR at, say, 16:00 to fly back to France the next day. We were earlier than planned at PHX and there was an earlier flight to ORD.
I asked if we can take that one - no problem. It is only when the planse started and the crew announced that we are flying to Portland that I thought WTF??
And this is how I discovered that a flight labelled A to B in the US can actually mean A to B via C where C is on the other side of the country. Kinda our city bus or underground... :)
We met very nice people, though, and I had an interesting discussion about the US. My son discussed with a lady in another row and she wanted him to meet his daughters when they will be in Paris :)
Ah yeah, if you were flying Southwest and did a flight change at the airport and you didn't pay for upgraded boarding, you would have been put at the end of the line for boarding.
I too tend to have interesting random conversations on Southwest flights, especially when flying alone. My hypothesis is that since people get to choose where they sit, they often end up picking where to sit by the vibe others are giving off, and it's more conducive to conversation.
The way to do southwest is not only to check in 24 hours before the flight, but also to book a flight with a nearby stopover where you continue on the same plane. When the other passengers get off, whoever is left on the plane can go sit wherever they want. Grab yourself a front row seat right next to the door.
You can even get off the plane to look around at the stop over airport, you just have to sign out with a stewardess. Then you get to board first. Like first-first, before the preboarding/military/babies. Then everyone at the boarding gate can imagine what a big VIP you are.
That was done at some point by Ryanair or EasyJet in Europe.
Three were riots, blood and tears and they got back to numbered seats