DisplayPort++ technically supports conversion to other formats including VGA through a passive adapter.
The main reason, IMHO, is that schools, universities, and meeting rooms in businesses were all wired with VGA to the projectors.
Laptops seem split between HDMI (for personal laptops, multimedia use) and Displayport (business laptops, largely. Toshiba has some that only have DP and VGA out). Re-running all the cabling as a new digital standard would mean choosing between these two.
HDMI can't usually be passively converted to Displayport.