I mean it's the whole concept. It seems more about downing the monster and less about the survival of your team.
I don't know, they could have other modes in store but I had the most fun in left 4 dead when I had to fight hard to survive at the end of a map and getting swarmed with mobs, and leaving a buddy behind to get on a boat lol.
Yeah... I hear what you mean. I would always create "speed runs" or my own type of games with my friends in Left 4 Dead. Allowed for a lot more variety. That's what made Left 4 Dead stand out for me but I didn't like some other gameplay modes too. Love & hate sort of thing.