After many months of trying to build an effective force to fight in the Syrian civil war, the US has trained only sixty troops. Most Syrians are reluctant to serve in a unit that will be seen as controlled by the US. They likely will be regarded with suspicion by other rebel forces, perhaps even attacked by some.
Note that they are using American M-16s, not the Kalashnikovs more commonly encountered in the region. Ammo for M-16s is much harder to come by there, hence the troops will be reliant on the US. The Sunnis trained in Iraq are also being fitted with American M-16s.