I agree with you that the T&Cs of the card do not say you need to have actually flown to receive the points:
Get 10% Points Back When You Redeem
You will earn 10% of your points back as a redemption bonus, to use toward your next redemption, every time you redeem. There is no maximum number of TrueBlue bonus points that can be earned annually from this benefit. This benefit only applies to TrueBlue points redeemed from the primary cardmember's TrueBlue membership account. For benefit to apply, your Account must be open at the time of redemption. TrueBlue redemption bonus points typically post 4-6 weeks after your redemption.
That said, I guess it's theoretically possible that you could use your points for a refundable fare or pay the cancellation penalty and have the points redeposited before the flight date. In that case, they'd have to have their IT systems setup to properly debit the previously awarded points from your account. IME, JetBlue's IT competence is fair to abysmal, so I would not be surprised if they can't support the recoupment of the points, so they just wait until the flight is actually flown to avoid people gaming the system. It's just speculation on my part, but it wouldn't surprise me in the least.