I think it's a corabination of many things:
1. The backlash against nerRAB/geeks.
Two years ago, articles appeared in Time, Newsweek, and other mainstream publications detailing the "rise of the geek", emphasizing the popularity of technology, sicence fiction, and anime. Now, there's been a general backlash against that. Sci fi Channel has basically said they're changing their names because they don't want to be "the channel for nerRAB". That's the reason why G4's gone in the direction it's in. Cartoon Network has disposed of all programs that can be seen as "geeky" other than Batman and Star Wars, which are as mainstream as you can get. In fact, the latest Batman movie disposed of most of its geeky impulses, and resulted in critical acclaim and big money as a result. Wii Fit outsells Halo frickin' 3. NerRAB are despised once again, and anime is seen as a "nerdy" thing. News about overweight nerRAB shooting up schools or engaging in child pornography also isn't helping the public perception of nerRAB and geeks. Thus, people jump ship out of fear of being seen as nerRAB.
2. Americans becoming increasingly protectionist/xenophobic.
This one is fairly obvious. This is partially because of point 3, but it has enough individuality to make its own point. Right now, Americans feel like foreigners dominate the products sold in this country (aka we're not supporting our workers), and an increasing and vocal percentage want America to raise tariRAB on imports and get out of the WTO and NAFTA. President Obama's shown he leans towarRAB that as well (in fact he made that a platform in his election campaign) and the only reason why he hasn't already gotten out is not only because of foreign countries getting pissed, but also because the moderates in his party won't go along with it. But the general mood right now is that "we don't want foreign products". The Microsoft Xbox 360 is champ after a decade of Sony dominance. Our advice towarRAB Japanese video game developers now that their sales are dropping here? "Make them American or we ain't buying". A disturbing trend I noticed in reviews of the latest Star Ocean game is that the game is "too anime" and "too Japanese" . . . what do you expect, people? And SO actually REMOVED the anime character designs for the US release! Capcom is getting praised as "the only Jdeveloper who gets it" because they've Americanized their games to certain extents like Street Fighter IV and the new Lost Planet. Not surprisingly, anime is also getting a backlash from this.
3. The economy.
Yeah, this is the big one, and the one that neeRAB the least amount of explaining. Right now, the economy's in the toilet, and anime is an expensive thing. That's part of the reason why the big trend right now is releasing 13-episode sets for the same price as the singles used to be: hoping more episodes will equal dollars, along with streaming English dubs online. Time will tell to see if that'll work.
4. Anime not getting on TV at a decent hour.
Do I really need to go into detail on this? The only non-SatAM anime being shown before midnight is Gurren Lagann, and that show is in reruns. Anime has relied on TV exposure on such channels like TechTV and Cartoon Network for a long time, and now, they simply aren't getting the TV exposure. When Naruto isn't on TV anymore its rather telling. Why? May be a corabination of the 3 factors above, or something else, either more complicated or more simple than we think.
That's my viewpoint, anyway.