Well, I for one don't like dragging out games that are clearly already lost by one side. And by clearly, I mean: Marines having 1 node, aliens - 3 hives, all other nodes, tons of fades/onos, etc. Simple, Marines have no chance for a comeback. I usually expect such games to end with the Aliens just rushing the Marine base within 3-5 minutes after the last major event (failed PG rush, etc).
Too often, Aliens try to end the game, yet the Marines resist. Why? I fail to see the excitement in shooting a couple of bullets from LMG, dying, respawning, shooting some more bullets, humping the armoury a bit, shooting a couple of bullets again, maybe getting devoured.
And so on, for ~5-10 minutes... that really isn't what Natural Selection is about.
Of course, if most of the Marines are having fun while doing this - fine, let them have it. But I won't be one of them