The question that was asked was what their motivations would be for trying to build nuclear weapons in secret. First of all, it is not proven that Syria or Iran is or was actually doing that, and secondly, whether or not doing so is legal under the NPT is irrelevant to the question of why they would do it. If they are trying to have nuclear weapons, it is because they perceive the only country in the region who does have them to be a direct threat to their sovereignty and national security (and with good reason, since Israel has been calling for the destruction of both of those countries for many years). Which, I guess makes their motivation somewhat different than Israel's since no countries in the region had any nuclear weapons back when Israel got theirs. So Israel wants to have an offensive capability, and Iran and Syria are trying to establish a defensive capability.