Only because JFK died and it was a memorial project. If he hadn't died, Johnson (or whoever succeeded JFK in 1968 (or '64, who knows?)) would have gotten the credit, if we'd made it by '69 in the first place - doubtful.
Besides, if the president who proposes Mars will get the credit, that'll be Bush. The president who actually pays for it will lose.
Besides, if the president who proposes Mars will get the credit, that'll be Bush. The president who actually pays for it will lose.