Why arent project minions on dominion?

Probably for the same reason Pool Party minions were SR-exclusive: Riot doesn't think the rest of the maps are worthy of celebrating alongside SR.

That would mean that you play dominion. One does not simply play dominion.

I don't know how accurate LoLKing is, but if you check by monthly stats, Fiora has 14.3k games on NA, Lee Sin has 22.5k games on EUW, and Yasuo has 5.7k games on EUNE. If you count all regions Yasuo has a bit more than 42k games played. Daily stats alone Yasuo has nearly 3k games over all regions. And remember, this is only one champion, lots of people play other champions (such as Nidalee, Teemo, etc).

Now, this is significantly less than ARAM, where Ashe has 280k games monthly stats, and Twisted Treeline has Yasuo with 72k games (although remember that you only need 6 players for a game of TT, 10 for Dominion).

On NA TT, Yasuo has 22k games played. On EUW TT, he has 37k games played. He is the most popular champion on both servers. On EUNE, he has 9.8k games played. These stats are for normals. Ranked, Yasuo has 53k games on EUW, 28k on NA. Even with 6 players per game, Twisted Treeline has a lot more games played than Dominion when you factor in both ranked and normals. This doesn't surprise me.

Let's compare with Summoner's Rift, shall we? On NA, Vayne has 97k games in Normals, 438k in solo queue, and Thresh has 110k in ranked 5v5. On EUW, Yasuo has 99k in Normals, Vayne has 450k in solo queue and Thresh has 186k in ranked 5v5. There is reason to question these stats, however. The amount of normal games seem a little low.

Anyway, yeah. While these stats may be questionable, they do show that Dominion still has a player-base. Smaller than TT and ARAM and SR, sure, but on EUW it's not that bad, 42k games with one champion isn't that bad. And, you know what? I don't even see Yasuo that often. But according to Daily stats, he has 1600 games on EUW, and Zed has 1248. I suppose we can assume a few thousand games each day, at least. The least popular champion, Urgot, has 10 games, the second least, Graves, has 17.

You might object "I bet a lot of those are bots". Bots use Heal/Barrier, right? 2.2% of the daily summoner on EUW is barrier, 2.1% on NA.

So... We can assume that there are a few thousand Dominion games per day on NA and EUW.

Dominion? What's that? ;)