Because Napoleon's Russian campaign campaign in 1812. Russian troops were withdrawn from Serbia. Russia made peace with the Turkey in Bucharest which rebels didn't accept because of the unfavorable decisions for Serbia.
At the end of the summer of 1813. the superior Turkish army attacked Serbia from several directions. After a lengthy battles of Deligrad, Negotin and Zasavica (Ravanje), the Turks re-conquered Serbia. A large part of the population, with Karadjordje and other insurgents, went to Austria and Wallachia.
Turks in Serbia made harsh reprisals, restored their power and established the Belgrade pasha jurisdiction at the old borders. The resistance of the Serbian people was not completely broken. On the tradition and achievements of The First Serbian Uprising free Serbia was later restored.