Resistance to change and institutional intertia were the biggest hurdles. You have to be on the inside here to believe how powerful a force that is. It's incredible. The other more physical hurdles are technology issues (for the last 50 years, the "southwest day", an actual term that people use here with a serious face, ended at 3am central time) and labor contracts. The contracts are done and I think the new dispatch flight planning software will probably be the last big step towards resolving the tech issue.
You're right, though, for an airline with an aircraft problem, the simplest way to get more aircraft is to use the ones you have. Strange that it has taken this long. I hate flying the backside of the clock, but some east coast commuters will eat it up.