It's not that these techniques don't "work" it's that they are very expensive in terms of the resources I discussed, that ultimately boil down to something approximately like "national will to continue the conflict." If a state has an extremely strong will to continue, then they are going to consider some of these techniques more worthwhile, but it is still about costs in one way or another.

That's normally where the international system has an influence, through sanctions or simply refusal to support the conflict, or deciding to support the other side, etc. Intentionally killing civilians would almost always fall in this category, but israel has apparently unlimited will to do it and is effectively unsanctionable in the current political environment, so it will continue.

Anyway there are much more illustrative examples that prove the rule, for example landmines. They aren't currently considered war crimes generally, but they are extremely damaging to civilian populations during & long after the conflict, and most countries have signed the treaties banning them. The countries that never signed are exactly the ones plausibly expecting to fight a war soon: US, china, russia, israel, iran, india, pakistan. And now some eastern european countries have withdrawn as well for similar reasons.

So from that you can kind of infer that landmines are probably very effective at their military goals, in a way that eg summary execution of prisoners or bombing hospitals may not be.