Waivers aren't legally binding. The company gets nothing by providing feedback, and even if there's a small chance of a lawsuit, why take the risk?

I'd argue that the company does get something back, potentially. Many companies will say to come back after 6 or 12 months to re-apply. If they like a candidate well enough to really mean that, wouldn't it help the candidate to learn what they were otherwise weaker with so they can work that out before returning?

But that's a fair point about waivers not being legally binding.

Undoubtedly because that takes more time and money, for relatively little upside for the company, and often, relatively little upside for the candidate.