My theory is that when they continued the no middle seat occupied policy they had to kick some people off. I had reservations in Oct, I made mine early, then added one for my DH much later (like months later). When they said no middle seats in Oct, he got booted off the flight, I was not. They recently announced no middle seats in Nov.
I have SW flights in Dec from PIT. They just eliminated all non-stops so I now either have to change at BWI or Nashville. I probably won't even go, but I am looking at my options for switching from flying home on a Monday night to Tuesday afternoon.