Gaddafi had his problems but sol massively improved under him. Given we back plenty of much worse dictatorships, it wasn’t done for altruistic reasons. It was done because he was giving a cut of the wealth to the masses instead of to neocolonial powers. Incidentally, improving sol and education like Gaddafi was doing tend to trend to democratic transitions over time.
The open air slave markets were a direct result of the intervention. The US backed regime didn’t have a democratic mandate and didn’t have Gaddafi’s entrenched power structures and collapsed.