Ah ok, I had misunderstood then, excuse me. That is not unreasonable at all as a metric of success.

When you say professional, you mean philosophical journals, or what? My first thought would be the language - people aren't writing much response to him in English and German too? What is the situation like regarding interplay between the worlds of English language and German language philosophy?

I can see why his books might be popular with a lay audience, in that they're short, and quite manageable in terms of the images and sentences.