Syria was weakened by NATO supported terrorists such as ISIS and Qaeda branches. Slowly the country is getting rid of them. Hence trying to strengthen their military.
When Syria was engaged with internal terrorists, they had to tolerate the damages inflicted by outside terrorists (Israelis). Currently, the internal problem is being solved and the country is regaining its internal stability. Before all these events, Syrians had little will to return to fighting against Israel but after Israeli support for terrorists, they have every reason to consider it.
Syria itself is a missile producing country having produced different versions of Soviet era Scud missiles. Now that they are getting rid of terrorists, they take an eye for an eye from Israel. If Israel hits the cargo then Syria will bomb Tel Aviv.