HERCULES (1958) was a big hit worldwide. Naturally that led to a glut of these types of movies, no surprise there, it happens with every fad and type of movie- spies, westerns, sci-fi (I'm waiting for the brainless big budget action movie fad to die) you name it.
since there were so many of these movies released, the US distributors could pick the best of them to release to the theaters, and let AIP-TV (and others) release the rest directly to TV. Something Weird released a nice DVD of this a while ago, with a great print.
Alan Steel has no problem hefting one over his head, but how heavy would styrofoam actually be? The costume was probably pretty warm for those poor stunt men though.
The effects are actually pretty decent, and the movie is never boring, despite a five minute sandstorm towards the end.