Honestly - I've said it before - Walther does a crappy job at advertising and pushing the gun.
Uramex purchased Walther in Germany from what I understand, and they were/are an airgun company. They seem no not have a priority to push the guns on the US market. And, by counting on S&W to do the imports instead of doing it themselves, they seem to not be very interested in taking the bull by the horns. S&W would rather push their own products, I think.
Also, when the P99 first came out, it was priced higher than similar guns (other polymer guns like a Glock). I think they started off on the wrong foot. Since the P99's introduction, Glock just got stronger.
Now, the price differences between brands aren't that bad. But, it also depends on where ya shop. I've seen new P99s as high as $630-$699 at certain places....