Not the parent, but the geopolitical reasons why Obama chose to intervene in (say) Syria and not in (say) Saudi Arabia or Kuwait when those nations chose to machine-gun their Arab Spring protesters are pretty clear. Syria is Russian-aligned, Kuwait and Saudi Arabia are US-aligned.
So, too, are the reasons why the US refuses to act against Saudi-backed forces, or in favor of Syrian forces, or most blatantly by refusing to assist secular Kurdish forces (and risk pushing Turkey into Russian arms). Killing civilians has nothing to do with it, again see the Saudis or the Kuwaitis.
Or again, see how the US backed the military coup in Egypt, as they too brutally suppressed dissent. Gotta keep Israel safe, too.
From the US perspective, the whole area is a quagmire, which is why Obama didn't actually put troops on the ground. There is literally no one who is ideologically acceptable to everyone and actually stands a reasonable chance of winning the war. We backed our allies as far as necessary, including to the extent of brutal suppression of dissent if necessary, but no farther.
Obama's decision was that we're not going to get bogged down in another unwinnable war. Realpolitik at its finest. And all the while, the power vacuum continues to turn Syria into a bloodier and bloodier meatgrinder. Not that I have any solutions either - other than "don't mouth the slogans about democracy if you're not willing to back it up".
But again, all of this has been pretty clear for a while. It's really, truly no secret what Obama's position on this has been.