I don't think that it's Dominion's popularity that it's the problem — as has been pointed out, it is insanely popular. It's just that the vast majority of players are casual players who never enter a tournament, which is probably because Dominion doesn't have the kind of official support for tournaments that Magic does. Magic has a ton of tournaments that are very easy for casuals to enter, such as FNMs and pre-release tournaments, and then they have bigger tournaments which attract high-level players and motivate not-so-high-level players to become better at the game. Dominion has funky national championships with invisible advertising where one 4p base-only game determines the winner.
Since RGG is a small company, it might be too much to hope for the same level of IRL official tournament play that Magic has. However, it doesn't take a big company to have lots of tournaments online, so if Making Fun wants to implement a tournament system with smaller tournaments to attract casuals and bigger tournaments to give casuals an incentive to stop being casuals, it could happen some day.
