I dunno. It's not like it's slavery. The players know full well what they are getting into when they sign for Chelsea and they also have to accept a loan offer from another club so Chelsea can't just "farm out" young players at will. I'm sure they are also getting handily compensated for any inconveniences.
Anyway, I'm not sure their policy has paid off. Hardly any of their youth players ever get a chance to play for the first team and there's been many examples of young hype jobs going there without profiting in terms of their development. A guy like Piazon was hailed as the next Kaka but where is he now?
Maybe Chelsea earn a little when they sell these young players but I doubt they profit when you put together all their expenses.
Looking at all these Chelsea youngsters who seems to get lost after loan after loan it puts into context what a remarkable determination Joel Campbell must have to come back after all these loan spells and perform like he does currently.