Because it was boring and mediocre. Rather than providing either a huge open world or a tight metroidvania kind of world, it had huge open areas of mostly flat terrain connected with corridors, and you could not jump from anything other than predetermined areas. You could just walk in one direction till you stopped like Skyrim, but it wasn't as interesting to explore. The story missions are few and far between. None of the characters are engaging, and there are a ton of uninteresting or alright quests instead of interesting ones. The lore is certainly miles deep, but the characters are definitely not.
The combat is decent as far as action games go, it's better than Origins Wolverine or whatever, but it isn't as good as something like Bayonetta and lacks the boss variation and enemy patterns of a God of War. And those games don't need to keep their systems interesting for the length of an RPG campaign, yet you learn way more moves and new abilities in Bayonetta than you ever do in Amalur. Even at its biggest boss fights, Amalur is bad. Now, some action RPGs have worse boss fights and action systems, like Fable 2. But if you compare Amalur, Skyrim and Dragon's Dogma, who all have a powerful dragon as one of their final bosses, what is the fight like? Amalur has QTEs and fighting clones of your classes that the dragon summons while hovering outside the stage, occasionally sticking it's big head in for a bite. Skyrim has a dragon which is similar to every bloody other dragon you've beaten in the game, save for a new spell. In Dragon's Dogma? You run from it, you fight its head, you platform while it's shooting fire at you, you QTE on its back, and then it's down to a huge arena and you can fight it however you like. And you get to jump and climb on it's back, not just roll around on the floor. That game has a ton of problems on its own, but the combat beats Amalur.
I played ninety hours of Amalur, including DLC, but I'm not going to celebrate it. It started out winning me over with it's nice look and first area, but in the end it was a simple game to play while listening to podcasts. Around the 40 hour mark I got so tired, like DanielBrown, and just ran through the last continent. Maybe hard mode would fix the easy gameplay, but it wouldn't fix the enemy variation in an area, the boring writing, the boss fights or the lack of fighting moves or exploration options. It isn't exactly bad, I think it has way better combat than Dragon Age 2 for instance(and 1, but that's not action, it only looks like it is). But I totally understand why other RPGs got more recognition. Maybe everyone were dissappointed that the creator of Spawn and the musician behind Banjo-Kazooie made something this generic, too. Even the intro music sounds more like Spider-Man than Grant Kirkhope.
(I liked how Amalur handled the class system. It meant I could be a wizard with a huge hammer that was actually effective.)