Sounds similar to Charlie Wakefield. Chelsea have a huge squad of players who are good at youth team level and an entire squad of loanees (they even employ Paulo Ferreira as their 'loan coordinator'), leaving players who were talented at youth level to not really progress in the adult game.
I have heard on the grapevine that some of their youth players look back when they're older and regret wasting their early years at Chelsea
Most clubs have only 1 or 2 in each age group who they think have a chance of making it and they are given first team opportunities early on at 17 or so
Chelsea hoover up so many talented boys that their youth sides are packed with kids who would get a chance elsewhere
But at Chelsea the owner is only interested in short termism and would rather buy other club's youngsters than give one of their own an extended run
It changed briefly under Lampard so two or three forced their way in but that's over now
There are loads of examples of young players ditched by Chelsea who thrived if they got out early enough. Declan Rice for example
It could be that Colkett is a Charlie Wakefield
But he might also be a Dujon Sterling
Time will tell