The only reason that this opportunity exists to swoop in and forge a transaction is that the reward in question is a reward for fundamentally breaking a weak ve

The only reason that this opportunity exists to swoop in and forge a transaction is that the reward in question is a reward for fundamentally breaking a weak version of the cryptography underlying the BTC blockchain, the technqiue for which happens to have a second mathematical weakness. No other transactions are subject to this weakness, and it's this puzzle which proves that.