US intervenes in Libya, but not in Syria militarily. Syria doesn't have oil, I think it's pretty obvious why the US or any country for that meddles into any other country, common interests.
- Syria also has a population more than four times the size of that of Libya, and the population is more spread out.
- The Syrian army is the third biggest in the Middle East, with Anti-Air Defense being a separate branch. They are also backed heavily by Russia, who provides advanced anti-air weapons. Libya's military equipment was rather outdated.
- The intervention in Libya was under a UN mandate. Muammar Gadhafi (or however the heck you decide to spell it, there are more than eighty "official" ways to do so) had publicly announced a bloodbath in Misrata and was bombing his own population. It was pretty clear that things would go down the drain quickly unless somebody did something. Al-Assad actually enjoys some support in the population, unlike Gadhafi at the time before his fall.
- Libya has a relative proximity to France, Malta, Greece and Italy. All places suited for bases from which air raids could be conducted. Neither of the neighbours were likely to object strongly to NATO intervention. Syria is smack in the middle of the world's powder keg, and air raids would involve flying over troubled territory.
- Libya had no close allies in the region. Not after the fall of Ben Ali in bordering Tunisia, at least. Attacking Libya wasn't likely to involve any neighbours in the war. Attack Syria, and suddenly Lebanon and Iran shows up for the fight, and Russia is likely to cut diplomatic bonds all over the place. Then Saudi-Arabia and Bahrain pick up their sticks as well, and the situation may escalate quickly.
- What we learned from Libya was that weapons involved in the revolutions go all over the place afterwards. Lots of heavy equipment is missing from Gadhafi's former arms depots. Most of it probably went to Mali, where it is being used in the pseudo-civil war they've got going now. Syria also has chemical and biological weapons (the poor man's nukes) which nobody really wants to lose their hands on, as well as weapons that can easily down passenger aircraft. At the moment, the Syrian army has relatively good control of those weapons. Attacking the country would stir the kettle too much. At the moment, it's still possible that Assad is removed without too much fuzz (unlike Gadhafi, who fought to the bitter end), and the structure and control of the armed forces survives the civil war. As we learned from Germany and Iraq (albeit with 60 years in between), it's a lot easier to deal with a defeated nation with their armed forces intact, than a country where the military and their weapons are scattered all over the place.
TL;DR: The situations in Syria and Libya are vastly different. The question (bomb or not) might be the same, but the implications and logistics of bombing Syria is a lot worse than it was in Libya. It's not as simple as the oil.
