So the software can have a wide release without the first-10-people-to-download-profit-handsomely drama. If the code was available in advance, people would start mining right away. Although this raises the potential threat level that tacotime is fooling everyone and putting in a wallet stealer for every *coin out there for everyone greedy enough to just run the binaries at launch. I'd say that probability is pretty low, but it would be hilarious.