It's a really enjoyable/good movie. That's literally the only reason movies get popular like this.
I suppose I could go into the reasons WHY it's so enjoyable, but I don't really have time and I think other people have explained it here already. The movie was well-crafted and had a story you could really get invested in, combined with an interesting cast of characters and a surprisingly good twist or two.
That it appeals particularly to furries is reason why the fandom's been so excited about it, but furries are honestly a drop in the bucket when it comes to the people who will/have watched it.