I suppose that kind of thing has been brewing in the backlot ever since Charlie Higson did Young Bond and actually made it a success. Eon must have had numerous offers during the young adult wave of Potter/Panem/Twilight and probably still gets a pitch a month from the streaming heavyweights. That’s not to say Eon seriously considers anything in that vein - but you never know what the future might bring and having the potential to open this particular drawer is no doubt a plus.
Why don’t they do it then?
Probably because it would be difficult to exert the same amount of control over the finished product they have over the films. And once you give up control over an asset you seldom get the chance to win it back.
So the potential to do something like a tv series - Young Bond or War Bond or Special Envoy Bond or whatever - is likely worth more to them than actually doing it.