There is something to be said for the idea that perhaps we don't have anyone ready for the Prem in that position? It could, and I admit I am speculating, cause confidence issues for our young wingers if we put them on the big stage too soon and they get thrashed badly and the crowd turns on them.
In general, I agree that we should focus on our own talent, but if we really don't have an option ready to step up and play on the wings, then we have to bring someone in, and if we believe in our youth, then we probably would rather bring in a loan to cover until the step can be made rather than buy someone and deal with figuring out how to squeeze the younger players into the team when they are ready.
Some players just aren't ready as early as others.