The capacity to keep secrets, even at the state level, takes a level of mental maturity that few are capable of. So many are thrilled by the idea of knowing something few other people know to a degree that they paradoxically want to make it something everybody knows. Journalists take advantage of this and collect and share leaky sources amongst each other. The reason for the leaking is most likely just human nature.

That said, the existence of the state of Israel is such a contentious topic that the leakers may have been motivated by politics as well as the above, sure. But I doubt state-level agencies are condoning the leaking here.