It is difficult to write a rule that works perfectly all the time. It is even more difficult to write a concise rule that does so. And complex rules potentially

It is difficult to write a rule that works perfectly all the time. It is even more difficult to write a concise rule that does so. And complex rules potentially increase the cost for everyone. I think this particular behavior isn't as bad as people make it out to be. I would assume this increases overall airline industry's carbon emission in tiny fraction while the rule probably prevented the tragedy of the commons for those slots.