[toast0]

If you're bumped, it's the same disruption either way, but booking the capacity of the scheduled equipment within predicted conditions is not unreasonable and it's hard to see what they could do to avoid the situation where some passengers aren't going to be able to fly on their scheduled flight.

If the weather changes such that the maximum weight is reduced, or the plane needs to be replaced and only a smaller plane is available (Southwest flies three 737 variants, one which has quite a few less seats), or a seat is broken and can't be fixed without a greater disruption, they don't really have another option than bumping passengers or always leaving many seats unsold.