Money;
Whatever organization was holding the event would have to pay extra money to use the space longer.
Money > Chess ....
I don't know if it's about the venue space or what have you but I think some of us are forgetting that sometimes blitz is a treat for others to watch. Even a chess layman can get a kick out of trying to keep up with someone's blitz moves.
Say what you want...but a GM's blitz has more logic and sense in it than my standard game...it's a treat sometimes to marvel at how fast they can take so many things into calculation.
Of course, now it makes sense...