LOL what kind of reasons do you expect? They liked the game. If you wanna know what they liked, plenty of threads about it in the DmC section. My personal bet is because DmC fairs better compared to DMC1, 2 and 4, cause 1 feels very archaic (in the combat system above all), 2 we know the story, and 4 was disappointing for many.
And frankly, shouldn't be a surprise. This forum is for Devil May Cry in general. It's normal that there are DmC fans here, one of the few places where you can actually even discuss DmC. Dunno if you've noticed, but if you talk well about DmC in most places that are not here, you get more wrecked than a guy in a hive of Xenomorphs.
Obviously I'm not saying situation here is all good and argumentless, but still it's pretty fair in comparison.