First of all, who are "these guys" ? Also, making meth is simple enough, but there REALLY isn't a whole lot of clandestine opioid synthesis going on. Hell, I'd venture to say that there's almost none. As for benzos, it's not impossible to synthesize them illicitly, but the fact that they're so common already when the entire supply is diverted from legitimate sources, there's not a big market or profit potential, you've got competition from every kid stealing his mom's valium script.