We're at an impasse and I'm going to agree to disagree here. Specifically on them being used without much regard for accuracy because that just seems nonsensical. The whole goal of shooting at a thing (or a person) is to hit it (or them). Firing at random just wastes ammo and doesn't help the war effort. As for "used to excess", how do you define what's excessive? Certainly an artillery battery will not keep firing once the target has been killed. And as for the cluster munitions being devastating to civilian populations well after the war ends, so are mines and no one is complaining about either side using those. Not to mention the Russians started using cluster munitions first so if anything this is just achieving force parity.
Easy. A single artillery shell will likely miss, meaning you need to use more of them. Cluster munitions hit a wide area, and therefore you need to use less of them. It's like using a shotgun vs a rifle. I'd highly recommend this video for more information.
Cluster bombs are highly effective at what they're using them for. And the alternative is mines. Neither is exactly civilian friendly, but at least this way the failure rates are lower and the bombs you're leaving behind are actually being targeted at something instead of buried and forgotten.