Hours-long flight delays sitting on the tarmac...
I know the airline uses federal regulations as an excuse.
I know that airports are busy etc..
but -- I also know that it isn't impossible to get people off of an airplane, even if there aren't gates available (and, they can be made available -- if nothing is moving, they can pull a plane back, let people off, and put the original one back in place -- it would take 15 minutes...).
I'm sure there is some set of BS reasons -- a combination of how fees and "on time" departure is calculated.... but, it's simply irresponsible to hold people that long.