South Ossetia is nothing. Its a sparsely populated mountain region with few resources and no value. Its only value is as a defensive barrier to Russian aggression, and as such its a valuable piece of territory, like the Golan Heights in Israel.

South Ossetians have been quasi independant, but SO is not totally non-Georgian, and there are dozens of villages with Georgian populations, that the Georgian government wants to protect. Naturally, the Russians and Ossetians want to drive those people out.

Towards that end, the Russians have been giving aid and support to South Ossetians in order to keep the area under friendly control. In doing so, it preserves Russian options, and they can steamroll over the Georgians any time they please with few casualties.
Without control of South Ossetia, Russian forces would face a stiff fight to even push through the narrow roads and gorges of SO without taking huge casualties.

Georgia should retain control of SO, its their land. Russia should have a say in how its people are treated, but this is not the way to go about it.

Russia has overplayed its hand here, and it will not be the victory they had hoped for when the US sells Georgia more ATGMs and attack helos.