Rally in the US was nearly dead in the 2005ish timeframe after most of the factory efforts pulled out(Mitsu, Dodge, Hyundai, etc.) and before Block, Pastrami, and later Mirra joined the fray. Hate on those guys all you want to, but their names and the money they've brought into the sport saved rallying in the US. Without them, you wouldn't be able to hate on them while you watch them in the X-Games right now.
At the end of the day, Subaru's #1 goal is to sell cars. A bunch of D-list celebrities are going to bring in more spectators and thus expose the brand more than a bunch of talented guys from Europe that you've never heard of. While they're awesome drivers, the casual fans don't care about L'Estage or Higgins. They come to see Block, Mirra, etc.