I dunno about you but even as a kid I always preferred the bad guys. They usually looked cooler/were cooler in the show. I'd much rather have had a bunch of badass bad guys and a few good guys for them to beat up on. Or even if kids do prefer good guys, they'd still need bad guys to beat up on, I mean the hell are the good guys gonna do without villains, fight eachother? Honestly the only real explanation I can see that fits is parents (at least moms, I doubt most dads would do the same) would rather buy good guys for their kids than bad.