>>10737835he was thought to be unreliable and had more drug issues than Shawn at that point. By the time Shawn became a problem in that regard he was too big of a star to get shitcanned like Marty did years before.
I've seen it said by a few sources that Marty was initially pegged to be the star. Not sure if that was initially when the WWF initially signed the Midnight Rockers from AWA and they had their first brief stint, or maybe even in AWA, or at the time of the pic in your OP. Been a few years since I remember reading that. It makes sense though, if you listen to their AWA promos Marty is much more comfortable than Shawn is and basically is the one carrying him when any talking is done.
