TLDR; people are taking advantage of the southwest "pre-boarding" including with fake disabilities and then snagging the premium seats before the people who have paid to board early can, and people are mad. (See article below)

Here's the solution: Let the pre-boarders still board early, but they have to go all the way to the back of the plane.

I have never understood why people are in such a hurry to get ONTO the plane so you can sit in your tight seat and wait for everyone else to board. There are a few exceptions to this like when there is limited overhead space, or when you're in first class and they will give you a drink but even that is happening less.

I'm always in a hurry to get OFF the plane. Either I want to get home or get to the hotel or I have a tight connection and I want to grab a bite in between. And then you have the people who are in no hurry to get off who ruin it for everyone else. Often elderly people or people with kids (see pre-boarders). Getting off the plane should be so fast, but it never is, and one person is always the bottleneck. Unlike getting on, all you have to do is grab your stuff (which you should already have ready to go if you are socially aware) and get off. If you are in the category that takes forever because you have to corral 17 stuffed animals and juice boxes and pacifiers, you should be in the back of the plane anyway.

So Southwest can turn a bad situation into a good one. Since they have no assigned seats anyway, they can take those pesky folks who aren't in a hurry to get off and let everyone else go first.