You need to note the current Syrian conflict had started with Arab Spring while the Turkey crisis was caused by a coup d'état attempt. As @SteveMelnikoff explained, the US government didn't like the current Syrian government and actually supported the Arab Spring as follows.
...He (President Obama) contrasted the ideology of al Qaeda leader Osama bin Laden, recently killed by US Navy SEALS, with that of pro-democracy protesters in the Middle East and North Africa, saying: "By the time we found bin Laden, al Qaeda’s agenda had come to be seen by the vast majority of the region as a dead end, and the people of the Middle East and North Africa had taken their future into their own hands." Obama praised the demonstrators, comparing their efforts to bring about reform to the actions of the Boston Tea Party and Rosa Parks in American history.
The situation in Syria is completely different from that of Turkey. The US wanted and still wants to see the Syrian government overthrown, but it never wants any instability in Turkey which is very important for the US interests.