There's not much reason to replace good functioning governments. There are some examples, although typically they are foreign-backed regime changes masquerading as revolutions.

Good and functioning are not the same thing. Look at North Korea. It's definitely not a failed state, but it's also about as far away from a "good" government as you can get.

For most revolutions, the state needs to be unable to maintain control over it's populace. The ones where it can still maintain control is where it gets bloody.