You cant not imagine Jose Mourinho doing that? Let me clear it out to you. Lvg and jose mourinho has very different plhilosophies of playing football and requires different player profile and player characteristics for each position. Jose mourinho's philosophy of football which is very similar to united's philosophy needs hard working young players with great workrate energy and physical development in player charectersticts in this league with off the ball work rate off the ball attacking space players similar to a cristiano ronaldo or bale or danny welbeck for instance . Young players have rarely got this type of stamina and physique specially in attacking or defensive positions . If any player young player suitable to his player charectersticts comes by jose will be happy to play him and trust him even in big matches like varane and kurt zouma. The lvg philosophy is more slow and posession based game that requires less of the work rate of the ball instead play like a coherent unit with every player doing his job with high skill so young players are easy to fit in those player profile charectersticts. TFM might be struggling to adapt to jose mourinho's philosophy like shaw martial mkh struggled.
More over Lvg Sir alex Pep guardiola luis enrique johan cyruff any many more successful manager have themselves been former players in their younger days, so they know how to better manage the youth and give them confidence to step up because they have gone through the same in their younger days, while jose mourinho has never been a player himself in his younger days he's just a good manager who picked up management skills from bryan robson and lvg himself in barcelona as he took training for them as Rui faria is doing with jose mourinho. That is a difference between player turned managers and game managers. A player turned manager knows how to build a youth player and what direction he needs to work on to become a successful player , a game manager's job is to manage so he picks up the best suited instead of building one.