Russia annexes half of a sovereign country and wants to topple the democratically elected government in favor of puppets, so they can defacto also rule the other half of the country.
We have no treaty or obligation to send in troops. When an Allie does something wrong, we are not obligated to help them. What are we supposed to do .. invade and start killing Russians? Does anyone think we should throw ourselves on that sword? Allies work both way. When they do something wrong and get themselves into trouble, it's not up to us to bail them out.
Did they really think they could escalate the situation, with no immediate need, and that Russia would do nothing in response? Did they think that Russia was a Paper Tiger?
Russia wanted an excuse to invade and Georgia provided one.