So on what evidence are you suggesting these players are ready for the step up to the 1st team ? Doing well against similar and in many cases poorer opposition each week is a million miles away from playing against a premiership team every week. If they were good enough they would get their chance, the same way Cadden , Campbell and others before them did.
The reality however is that the vast majority of that reserve side will never make it at the top level, so I am sure if Crags, Hammell or SR thought a player was ready and able they would get the chance, until then we need to bring players in.