Maybe because it has a different taste that does not go well with most of the players' flavor. I personally find it to my liking, despite many other people. I think it has some nice combat mechanics. Especially the fact that two handed weapons are much more slower and heavier. The only thing that is broken are spear-type weapons really.
Some reasons why I like fire&sword:
-There are many different yet balanced weapon choices for duels, save for spears
-Awesome captain co-op mode
-Single player is more fun than warband, because the elite troops are unlike the overpowered mamlukes/knights of calradia. You have to do some form of tactics, other than charge.
-Bombs are very fun to use
-In siege mode, the defenders I think has some kind of health regeneration.
-The fact that you can do something like couched lance with spears and pikes on the ground if you crouch.
... maybe some other factors I can not remember
Many people like Napoleonic, but I find it pretty boring. Yes Napoleonic is very more realistic compared to fire&sword. But I find myself having more fun with fire and sword, even with those overpowered spears and fast-deadly-overpowered hussar lances. Yet, I never say "Napoleonic sucks". It is just not my cup of tea. I have respect for Napoleonic players after all.
