Apparently the reason Firefly and quite a lot of other productions used it was that it was the last large set of decent quality sci-fi costume armor produced that wasn't TOO iconic like with storm and clone troopers.

Basically immediately after Starship Troopers if you needed more a few sets you'd just do it digitally, so all the down stream productions just traded that set between them and modified it bit by bit.

Supposedly some bits and pieces are still in use but they've been cut down into components.