[justin_vanw]

Since he considers it not ethical to continue, my guess is that there is some kind of government action attempting to force them to sniff or backdoor the service.

As for why he is announcing he is shutting it down rather than just pulling the plug, pulling the plug may well be considered obstruction of justice, but just refusing to donate materially can't be prevented by the government. It may well be that lawyers have advised him that by announcing his decision to not participate it gives the government reasonable notice to be able to find an alternative or take some action, and counting on there being no practical way for the government to respond without revealing that they are involved.

Edit: It may also be possible that he has become aware of a 'looming' threat to de-anonymize the service but can't speak of it, and he is announcing that he is pulling out since if he is subsequently compelled not to pull out it will act as a canary.