I was at Texas A&M from 2008-2012. HvZ started there in Fall 2009, and my first game was in Spring 2010. We had 2-3 games a semester with averages around 250-300 and a high of over 1000. The over 1000 person game happened very early on - it was the second game at A&M in December 2009. As time went on, it seemed like attendance really dropped off. Part of this was due to the experienced, passionate players getting into upper level classes and graduating. Part of it was due to our mod team all being on the quidditch team and not having enough time to devote more energy to advertising HvZ.
I returned for two games in the fall of 2012, but the lackluster attendance and some gameplay tweaks by the new mods made it not worth the 4 hour one-way drive and I haven't been back since. They are still running two games a semester. I didn't get a count for the last game they ran, but the one before that had only 33 players with an average of 10-15 for missions.
One of the tweaks the mods made that dissuaded me from returning was that they implemented a "winner" system for humans. In all the games prior, if zombies killed all humans at the final mission, zombies won. In an attempt to draw in competitive players, the mods changed it into a system where the final mission was always just a killbox and the last three surviving humans won. There was no incentive for zombies - basically, if you became a zombie you lost the game.
This combined with the advancements in NERF weaponry really hampered any chances for the zombies to effectively play. Zombies resorted to ambush tactics, but eventually with the dwindling player count, it became a burden to try to set up an ambush when there were maybe 20 humans and 10 zombies on a campus of 80,000 students. I presume zombies developed a "what's the point?" attitude when facing the fact that they could wait for hours and not see anybody and when they did, they'd have a more reliable, fast-firing weapon than the mavericks of old.
During late 2011 and early 2012, I tried to get a little more involved in attracting a new young playerbase. It seemed like nothing we did really worked though. Our attendance numbers slipped down from 200 to 150 and then even lower. I still don't understand why. I would think that at such a large campus, more people would at least be interested but the numbers never really swelled back up. Maybe we didn't advertise as effectively as I thought. Maybe people just didn't see any. Maybe the cultural obsession with zombies got a little tired.
I don't have any real answers to why Texas A&M's game has effectively died. Like toruk said, the NIC as a whole has seemed to have quieted down quite a bit. I personally haven't done anything nerf related in any sort of capacity for at least a year and a half. Maybe that is the reason. Maybe A&M was too large of a campus. I am close to UT Tyler and they seem to have a pretty healthy game there. Or maybe its just a getting the right people to run the game at the right time kind of thing. I don't know.