Syria plans to join the 2015 Paris agreement

Apparently Syria plans to join the 2015 Paris agreement along with Nicaragua. Makes the US the only country not joining. There are tow things making me wondering. Is Syria now doing anything to oppose what ever the US is doing? Why would they (and Nicaragua) suddenly care? May be it just feels bad to be among the few countries not signing, bad to be outcast? And why didn't they sign earlier? Both are not among the major polluters, why did hesitated? The other thing is what would have happened for the decision of the US if not Trump, but Obama, even Bush, were in charge? May be they'd joined? If, that would be just another indication that the Trump administration seeks to be isolated from the rest of the world. Possibly trying to get back to a state from the 30s before the US joined World War II, where the US didn't really cared what was going on in the rest of the world, minding their own business.