While the cap space is definitely not a deterrent, it's still also a question of what you think puts you in the best position to compete while developing that QB. There's good reason to believe Fields will leave you in a better position to compete than those FAs (thus also put less pressure on rushing the rookie), still be a tradeable asset after year where the others won't (potentially more, potentially less) and save 8-10(?) million.
Of course it's not without risk, whether it's questioning Fields ability to stay healthy, risk of regression, and lockerroom concerns, but none of those should also be non starters, IMO. Though history tells us the lockerroom part tends to be treated as a non-starter. So realistically I don't expect it at all. But I think it's interesting internet forum filler to chat about lol