I don’t know if this has ever been covered, but what was the reasoning behind Dusty Rhodes joining the NWO? 

What, kayfabe or legit?  I think the kayfabe reason was something about Dusty being bitter at WCW not getting the job done and it became a "If you can't beat them join them" scenario, but I don't really remember the details there because it wasn't exactly a long-lived idea.