The U.S. military has many types of aircraft that are developed and fielded for a specific purpose, although many are considered ‘multi-role.’ The F-15C is not one of these.
It is specifically an air-to-air machine, designed for air superiority over a battlefield. It’s pilots are the part of a dwindling fraternity, the dogfighter.
The aircraft are not deployed in theater unless commanders are worried about an air-to-air threat, in other words, aircraft that can target American attack jets or other support aircraft which are not capable of properly defending themselves in the air against a credible air-to-air adversary.
Perhaps this is why the F-15C was not deployed to the Syrian conflict, or Afghanistan, or Iraq, that is until now.
ISIS has no air force.
The only reason for Eagles to be in-country, if you will, is because the Russian air force has shown up in numbers, deploying SU-30 air-to-air fighters at their newly constructed Syrian air base at Latakia.
Eight F-15C Eagles have been deployed to Incirlik Air Base in Turkey to complement an A-10 contingent already in operation.
The Daily Beast reports that the American fighter aircraft could also be used to enforce a no-fly-zone over northern Syria, to protect U.S. backed insurgents battling the Syrian government and ISIS from Russian ground attack aircraft. Perhaps the Obama administration is considering declaring a no-fly-zone after all.