That's because there is no compelling US interest... But there IS a compelling globalist interest, or, should I say, there are TWO compelling globalist' interests.
The first is the delivery of petroleum products from the ME to Europe. The Euro's may be mostly weenies, but they very much do want to be free from dependence on Russia's natural gas, which is much complicated by most Euro's suicidal urge to go REALLY green. (France, to their credit, has been half-way sensible by building nuclear power plants.)
Second is that, outside of nationalistic urges in the US, and Chinese self-interest, Putin, his admittedly corrupt cabal, and Russian nationalism, are a major stumbling block for the globalists. This is of course partially due to the energy issue above, but it is only one factor, here. Putin is simply not someone who can be pushed around. But Russia can be damaged / drained by tying them down in long conflicts, much as with Afghanistan. Eventually, with a conduit to getting ME energy to Europe, a major source of revenue to Russia now has serious competition, and Putin no longer has Europe under his thumb. SA (etc.) profit handsomely, at the expense of Russia.
The difference in Syria, as we know, is that Putin has an able ally in Assad, who has support from significant portions of the population, and most of the Syrian military. Assad, with Russian support, is not so easily rubbed out...
Meanwhile, there is an ideological bent in the West to remake other countries into a "better" way, regardless of whether the underlying conditions to succeed at this are present or not, and apparently ignorant of what those conditions are...
This is not the whole picture, but it lays out the basics. Putin surely sees it, and is enraged.
(I am leaving out, here, the "Iran Deal", which is so inane as to almost defy rational analysis.)
Now, on the one hand I think Putin is a monster, and he probably does need to be weakened, and perhaps even "kept busy" within Russia. Getting ME energy to Europe IS a good idea. But the globalists, our State Dept., etc., are not only bizarrely naïve (who could not predict the results of the "Arab Spring", or mass migration of Muslims to the West?), and largely silent about the human cost of all this mayhem (except what they can try to blame on Putin / Assad), they also appear to be confined in their thinking to a box that is, I'd swear, about the size of a pea.
Good God. I am pretty sure that for much less than the $$ cost of all this warfare, refugee migrations (and the consequences of those), and so on, the Gulf gas and oil could be piped to elsewhere on the Med. Sea and then short-run tankered to Europe. Or, build those nuclear plants. Or... well, you get my drift.
In the much more immediate term, I suppose an argument can be made that on a humanitarian basis, we should not abandon our "moderate" allies to slaughter or violent conquest. Righto. The Ukrainians would be amused. But, hey, bygones are bygones, eh? And never mind our role in worsening all this. So, fine: Make a deal with Assad / Putin to temporarily let up on the attacks, and we will transport anyone who wishes out of Aleppo, disarmed, and not to be re-armed, at least not by the West, or SA and it's allies. Anyone who stays or won't disarm is on their own. Of course this is a victory for Assad / Putin and a defeat for the globalists, so it probably will not happen.
“Meanwhile, there is an ideological bent in the West to remake other countries into a “better” way, regardless of whether the underlying conditions to succeed at this are present or not, and apparently ignorant of what those conditions are...”
Dubya and his neocon true believers with their ‘democracy project’. Apparently the sort of society that Iraqis would vote for never occurred to these geniuses.