Probably because Valve thinks, this games is not big/long enough to get it. There are many games, that don't count. Usualy realy cheap games or some with like 9000 Achivements in 5 min.

If this is the case the game will have a tag on the store (in the same place saying single player, steam achievements etc) that will either say "Steam is learning about this game" or "Profile features limited". The former option pretty much always happens to new games or those with only a small amount of players. The game doesn't not have such tags but I realize this post if old and may have changed. OP does the game still not appear in your perfect games?

Originally posted by RainbowDragonz:

If this is the case the game will have a tag on the store (in the same place saying single player, steam achievements etc) that will either say "Steam is learning about this game" or "Profile features limited". The former option pretty much always happens to new games or those with only a small amount of players. The game doesn't not have such tags but I realize this post if old and may have changed. OP does the game still not appear in your perfect games?

I just checked, it looks like it does show up now. So it's probably still worth 100%ing smaller games if there's a good chance they'll be verified in the future.