The last time Marvel tried to do a Silver Surfer series, he was practically relegated to cameo appearances while a couple of normal humans took the center stage. This was at a time when Marvel was apparently rationing the appearances of all but their most popular heroes. Remember the Bruce Jones run on Hulk when Hulk rarely appeared? Anyway, it turns out that people who buy superhero comics want to see the superheroes.
The failure of the recent Thing series is more puzzling. The writing was excellent, the artwork was pretty good, and the stories were mostly packed with action. The main difference might be that the Fantastic Four was extremely popular for the first 20 years, making it easy for a spin-off series starring the most popular character. The next 20 years of FF were a time of lesser quality, overall, leaving the Thing considerably less popular than he was in the 60's and 70's.