I believe TKoK did not win because some of the changes made to it since the revamp were a bit of a turn off for the hardcore players and it turned a lot of people off. The complete level design change was one thing, but it wasn't a big deal. However, the aggro system they added is what really killed it for me and other players. It used to be fun to try and pull one mob at a time because of the risky challenge of accidentally pulling more than one. Now, trying to aggro one will aggro dozens. It would be fine if it were easy to find a full game of people, because then such a system would make sense and fit. However, being that you'd be lucky to get in a match with 4 people, getting swarmed is easy and unsettling. Therefore, despite all the pretty systems and whatnot for it, some of the more simplistic features to it ruined it. I loved TKoK and feel it was the best ORPG for WarCraft III ever made. Now it has fallen to an uncomfortable state... they should've just left it the way it was, if ya ask me.
If you think about it, Against the Darkness was also a worthy candidate to win best 2009 Hosted Project of the Year. I see it being played on Battle.Net every now and then, and to be honest, slightly more than Diablo III WarCraft is played on Battle.net. It may just be the server I'm on, but ATD certainly shown it could win. However, I can also understand why it did not. Usually when I play ATD, the objectives and playstyle of the map don't quickly catch-on to some players, pretty much leaving them as live bait for the Death Knight. This was also a problem for TKoK I noticed. People were too stupid to figure out the map's simple systems. Also, D3W was more for a popularity vote (as was my mod's victory, for sure) because everyone has an idea of what Diablo III is and people seem to be attracted to good mods that try to replicate games; WarCraft III: World of Warcraft was another one.
ATD may be a good mod and might even be played slightly more on some servers, but it just isn't simple or easy enough for new players. It's focused more towards hardcore players it seems - which is fine! However, Diablo III WarCraft succeeds by being simple and good looking. All you do is follow a linear route, kill monsters and bosses, and make sure you're healing or protecting the healers. So, was it a popularity vote? Definitely. There's no justified argument I can think of that could prove otherwise. But was it at all about how the actual mod worked? Yeah! How else could they have gotten popular in the first place? D3W is personally more enjoyable than ATD (I suck at ATD though so yeah) because of its simplicity and how players don't ragequit within the first five minutes of the game. You can be playing with totally new players in D3W and get pretty far. Can't do that in ATD, from my experiences.