CFC stockpiling players and having 30-40 on loan during the season has absolutely nothing to do with players development for themselves, and has everything to do with generating another revenue stream.
Stockpiling and selling players is their response to replace Abramovich's previous contributions under FFP via player trading. It's also why they were investigated by UEFA regarding their influence over a Dutch feeder club regarding player selections, and why FIFA/UEFA are looking to limit the number of players able to go on loan each season to about half a dozen per club.
They have no concerns re selling the likes of Salah or de Bruyne because they buy and sell them before they have their breakout seasons, and in most cases they more than triple their money. Granted they do not get top value on individuals but they still sell for 20-30m, and it's the volume that is more important.