1) Counter-programming on Christmas never works. There is no "counter culture" on Christmas Day. Time and time again, films in the more hardcore vein, the geeky vein, which get put out on Christmas... bomb. This is not a Christmas Day movie.
2) Negative reaction to the first film. No connection to the first, you say? The entire opening action sequences takes place in a setting explicitly set up by the first movie. And it doesn't matter that there's no returning cast members - the mere knowledge that this is "AVP2" will be enough for most. Christ, most people won't even be able to tell the titles apart.
3) Lower budget and fewer creatures. Many, MANY fans complained that AVP just wasn't as EPIC as they thought the concept should be. The video games and comics have made the enterprise feel huge, and the movie kept things far more... contained. Of course, this is due to the low budget of only $60 million - hell, even the number of action sequences and Predators in the movie got scaled down between preproduction and the filming stage, because initially there were 5 predators, and the extra two Predators had additional alien fights that had to get cut. This movie's budget? $40 million, and with less Predators and aliens running around, you're going to hear that same complaint tenfold.
4) Idiotic setting/concept. The
other thing that I heard most frequently from the haters of AVP was that setting it on Earth and in the modern day was deeply stupid because of the screws it takes to continuity and the fact that it prevents things from being a big space opera. Well, if they thought setting it in the most remote corner of the Earth was bad, wait until they see Aliens and Predators running around a modern suburban setting in the heart of America! The characters even include some teenagers with high school love life problems, for christ's sake!
Frankly, any two of these would be enough to doom this thing. Altogether, you have to wonder if they're killing the series on purpose.