Because Natopia was too on the nose?
I hate cutesy, theme-driven ad campaigns. Marketing is all about inducing people to buy things that they would otherwise be indifferent to owning. Really good products/companies/sports teams don't market themselves. They don't have to, because the product speaks for itself. Sure, they advertise: "This is where we are; this is what you have to do to get us." but they're selling a thing, not a feeling or state of mind.
Bad teams dream up elaborate campaigns to distract from the product on the field. The Nationals can't just say: "Come see winning baseball at Nationals Park this summer!" because odds are on any given day, you won't. They can't say "Come marvel at the play of [established superstar]!" because apart from Zimm's slick fielding and flair for one dramatic game-ending homer per season, there hasn't been much to "Ooh" and "Ahh" over since Soriano left NatsTown.
In the absence of a tangible result, the Nats have to market the "experience" and the "community." That's fine, but it doesn't make a virtue out of the necessity to advertise around the team instead of advertising the team.
P.S. Whether it's a lousy catchphrase or not, sorry Caps fans, we've had dibs on "Get Your Red On" since the Nats-Cubs series of 2006.