Because people who work from chairs behind desks in climate-controlled buildings get all their excitement from stock phrases and edgy buzzwords?
Why do people say they have a fast-paced work environment when most of the employees move at exactly zero meters per second for hours at a time? It's all about marketing, and the lies we tell ourselves to prop up our self-image.
A rose not named Bloodpetal Olfactoryblastin' Extreme Transcendent Amazing Ultraromance Blossom does not, in fact, smell as sweet.
Postmortem doesn't (to me at least) imply failure. Specifically for games it's just a critical analysis of what worked and what didn't on a project for the purposes of learning for the next one.
I don't know if the phrase was originated by Game Developer Magazine, but it certainly popularised it's use within the games industry. The GD Mag postmortems are generally exceptionally candid and a great series to learn things from. See http://www.gamasutra.com/features/postmortem/ and the general archives at http://www.gdcvault.com/gdmag (I'm not sure if the website has all the postmortems that featured in the, sadly defunct, printed magazine).
At least in the games industry this is the typical term for the analysis of a project or process that has been finished, successful or not. Don't know about the origin of the term though.
You've got to love the way language evolves.... I mean, who was the first person to write every word in the sentences you and I are using right now! Who first said "you" ? Who first used the contractive "you've" ? Who first used the word "got" ? :)
