That's a unique opinion. Certainly for me, but this seems to have some wider critical consensus, his work as a documentarian is where he is at his strongest with some of his best works coming after this popularity arose (I'm sticking with Grizzly Man as the time). Since then he's made Into the Abyss, Encounters at the End of the World, Happy People, and a few smaller things which at least maintain the level of his previous work.
You're forgetting Cave of Forgotten Dreams
, which grossed over $5 million in the U.S. box office alone. I do agree with the crux of your argument, though. As for Manny Karp's side, sometimes I find myself wishing his modern fiction films (so much as that distinction accurately applies to any of Herzog's films, ever) were as good as what he was making in the 70s and early 80s, but it's hard to get too upset about that, what with the great documentary work he's been doing. Besides, Bad Lieutenant: Port of Call New Orleans
is pretty great.
Of course it is also worth pointing out that, shortly after Grizzly Man
, Mr. Herzog started popping up more commonly in mainstream entertainments as an actor: Jack Reacher
, and episode of Parks & Recreation
, that kind of thing. So of course a whole lot of people know him and his personality from that stuff, and have little to no idea of his work as a director.