Why are SPL teams not allowed?

to field teams in the third division? The game here is dying on its feet and competitive football every week for 16-21yr olds would give the whole thing a lift. Its fairly safe to say that every team in the SPL has talented youngsters that are being freed as reserve team football just isn't helping them develop. Teams like Barcelona don't produce so many brilliant young players just because of who they are, its because of a well thought out infrastructure added to the fact their second team are allowed to play in the lower divisions, so if its good enough for them why do the decision makers here think our clubs are above that? As a small nation with no real expectations on our clubs and national team Scotland should be pioneers in the development of young players , instead of the laughing stock we have been for years and are seemingly set to be for the next few decades.