Even if there were no absurd lawsuits (which certainly do happen), you cannot realistically expect 100% of your interviewers to be 100% educated and 100% consistent while giving feedback to lots and lots of candidates. The cost of a single suit is high enough that you must take the risk of someone ever slipping up with an off-hand comment very seriously. The only way to reliably prevent mistakes is to reliably prevent any form of feedback.

It's unfortunate because I'm sure many people I interview would appreciate feedback and I would be quite happy to give it to them. But, the aggregate risk across all candidates is too high.