Cobra was the first highly articulated 3 3/4" bad guy army out there. Star Wars figures of the 80's had five points of movement, and the only Imperial personalities made into toys were Vader...then after years, the Emperor. It was locked storyline, too. Once it ended, it ended.

Other toy line villains, well, Skeletor never had any generic troops in toy form, and his guys were all bunglers. They were too big for them to make too many vehicles, too. Besides, guns and army men are cooler than muscle bound guys with swords and magic, at least in my book.

Anyway, Cobra was the only enemy army that you build up, men and vehicles with an open-ended story, the potential for new characters, expansion. Also, it was big as you could make it, if you ignored the media.

That's where most knock-offs failed...they lacked cool villains. CORPS took decades to add bad guys, and still no "army builders" there. All those realistic modern soldiers...whaddya do with 'em?