Not everybody in Hollywood becomes a superstar, he worked steady in lead parts for around 20 years which is a pretty good career even if most of his films were B movies. There's probably not even 150 actors who can say that from the 1980's and 1990's so when you think of the thousands in the business he's done pretty good.
His looks if anything may have worked against him since there are very few super handsome men who become full-fledged movie stars, many are good-looking but in an average joe sort of way. I won't say Sam is a great actor but he is competent and as good at least as a number of much bigger stars. The "Flash Gordon" link probably also worked against him in the long run but he was able to move on in Hollywood better than the guys who played The Lone Ranger and Tarzan in the same period.

According to his biography, he is the CEO of Inner Cordon, Inc., an international security company providing diplomatic and executive protection for high profile clients around the world.
Sounds like an important company, so I am sure that it has been much more profitable for him than his acting career.
Christianity's GREATEST ally and BEST friend throughout history is Satan

If his voice had to be dubbed. it does not bear thinking what his real voice actually sounded like!
Its not as if Laurence Olivier was doing his film of Hamlet and the film studio executive thought, this may be the greatest Shakespearean performance on film ever. Let me get a bad actor in and re-dub his voice!!
Its that man again!!

Difficult to juddge his acting ability since his voice was dubbed by another actor in
Flash Gordon
.

It would be nice to see him in Ted. Not seen him in a role in years. He was a bit wooden as an actor.
Its that man again!!

He has a cameo in the upcoming movie "Ted".

Fair enough; I can buy that.
I want the doctor to take your picture so I can look at you from inside as well.

Because he was a bad actor. No offense meant to the guy, but it's true. He did have the movie star looks, but not the acting ability.