Because it worked out so well with zero blowback when we did it during the Afghan-Soviet war.

Via Al Arabiya:

The Central Intelligence Agency (CIA) has helped Arab countries and Turkey increase military aid to Syrian rebels in the past few months, The News York Times reported on Monday.

The report – citing air traffic data, interviews with unnamed officials as well as statements of rebel commanders – said the airlift now includes more than 160 military cargo flights by Jordanian, Saudi and Qatari military-style cargo planes landing at Esenboga Airport near Ankara, as well as at other Jordanian and Turkish airports.

CIA agents assisted Arab countries in shopping for arms, said The New York Times, adding there was a “large procurement” from Croatia.

It also said that U.S. intelligence officers checked up on rebel groups and chiefs to determine who should receive the military aid and that Turkey oversaw much of the program.

“A conservative estimate of the payload of these flights would be 3,500 tons of military equipment,” Hugh Griffiths, of the Stockholm International Peace Research Institute (SIPRI), told the paper.