Assad’s father used chemical weapons on the Syrians and killed something like 50,000 while Hussein had his weapons still in Iraq. This is nothing new.
It is nothing new. The Soviets equipped the Ba’athist Governments of both Iraq and Syria to be compatible with the Warsaw Pact military - including their heavy emphasis on chemical warfare. Both countries had large stockpiles.
Since such stockpiles are big and heavy, if you had to redeploy them, you might want to haul Iraqi stocks out by land or sea rather than air. Sea options were pretty much from Basra through a tight gauntlet of Western navies, or through Syria, where they could remain pre-positioned in theater, or be more quickly evacuated through the Russian naval base there. Pretty clear choice for the Russians.