The short answer is HDMI was mainly developed by a consortium of Stereo and Television manufacturers whereas DisplayPort was firmly always developed as a modern replacement for VGA.

Somehow, I trust the people in the computer industry to make better and more strict standards than I expect from the audio/visual industry. There's a lot more advertising fluff from those groups while PC stuff can generally be nailed down by checking benchmarks against each other. How would you even benchmark two different stereo systems? (If I'm wrong and there is a way to benchmark them, cool, please share!)

Anyway, yeah, HDMI was for "Home Theaters" and pushed by the industry that builds that kind of thing and DisplayPort is for computers, period.