Assad wasn't creating problems all over the Middle East, Iran was(and is).History says that Russian has had influence over Assad for decades. And when Assad was dropping barrel bombs on his people and using chemical weapons on them, they said nothing.
When Assad was creating a refugee crisis all over the Middle East, Moscow did nothing. Assad’s in a geographical location to cause havoc in Syria, Jordan, Iraq, Iran, Saudi Arabia, and Turkey. And Moscow either doesn’t care or approves of it.
To say Syria is not our concern is naive to reality in the Middle East.