They have? Russia is spreading itself thin. Their economy is in shambles. And they're a year away from exhausting their reserve fund. And to cover that, they've even taken to draining money earmarked for their pension and other social systems. Russia, under Tsar Putin, is in trouble. They were dragged into the middle east quagmire, and it's having disastrous effects.
You're looking at the short term negatives instead of the bigger picture. Russia wants to control the energy supply to Europe. The main pipelines run through Ukraine, so you can imagine why Russia is heavily invested there. When Ukraine tried to strong arm Russia, the Russians opened the Nord Stream pipeline to circumvent Ukraine in order to get into Germany. The Germans heavily rely on Russian energy and they were one of the only EU nations to voice objection to the original sanctions.
I don't believe Syria is a quagmire. I originally did but not anymore. The West's reluctance to forcefully eject Assad from Syria has proven to be their downfall. With Assad staying, Russia gained massive leverage over the region. They retain their port in Syria on the Mediterranean, gain a bigger foothold in the Middle East, and gain control of the flow of energy into Europe. The EU market is vital to Russia so while this temporary economic decline is harsh, the long term gains will be worth it tenfold.
There is speculation that the Syrian War is over pipelines. There are two major plans in place with competing interests. The first is a line from Iran that goes through Iraq and Syria on its way to Turkey and then the EU market. The second is a Qatari pipeline through Saudi Arabia, Jordan, Syria, and then into Turkey. This should help explain the Turkish role in the Syrian conflict. Originally, the US was dominating the battlefield and it looked like its allies Saudi Arabia and Qatar would win the pipeline so Turkey aligned itself accordingly. When the Russians stepped in and started taking over the conflict, the Turks realized they would lose out if they didn't support the Russians and implicitly the Iran-Iraq-Syrian pipeline. The Russian network could simply skip Turkey altogether and build a pipeline direct from Syria to the EU under the Mediterranean Sea. This should help explain the reconciliation between Turkey and Russia in recent months.
The two major flows of energy into the EU run through Russia and Turkey. Right now it looks like Russia will have a stranglehold on the energy infrastructure going into Europe. Now, in regards to oil prices, they certainly are low right now. Outside of America, most of the worlds economy is doing poorly. However, I think we've hit a bottom. Prices have bounced from the low 30's and are sitting right around $50 right now. The Syrian War is partially responsible for the rise in prices. The recent severance of cooperation between Russia and the US has brought even more tension and uncertainty which has raised oil prices. I believe this trend will continue and oil prices will stay on the uptick even with the glut of supply in the current market. I believe America is ok with the situation in Syria because it helps our energy industry tremendously. The Saudi's started a price war to retain their market share and its blowing up in their faces. They tried to bankrupt Iran and Russia by oversupplying the market with cheap oil thus driving down prices. They used this same strategy to put US and Canadian shale producers out of business. The Saudi's strategy worked for some time but now they're losing control of the situation. They're losing their Qatari pipeline, losing control over OPEC, losing their grip on the Middle East, and losing their proxy war with Iran.
TL;DR While the Russians are losing economically right now, their bets look like they will pay off handsomely in the longer term.