edit: I'll argue instant feedback is even more expensive and risky. It's not coordinated, potentially duplicative, may impact/contaminate later rounds, and may not be complete or representative of the interview as a whole. Engineers aren't known for being naturally HR/legal-compliant, and having multiple expensive engineers spend time doing things not in their typical skillset that's typically done by a single resource that specializes in said skillset doesn't sound cheaper at all.
Either something like this is being up collected and articulated up through the decision points in the hiring process, or the decisions are being made on a fuzzy basis that can't even be explained internally, which presumably represents a risk that decisions couldn't be properly justified should a candidate suspect discrimination and pursue a claim.
(This is especially true for any kind of exercises, btw. If an employer asks me to do some, I am going to screen them on whether they have (a) complete reference solutions with (b) numbers on how long it took to complete each and why they're confident those numbers are reliable(c) a written rubric for evaluating candidate solutions that (d) they'll agree to share with me when we're done.)
...Or, you know. Don't be that guy. Candidate, candidate, candidate--depersonalizing language for depersonalized processes. How about person? These are people you're talking about. They matter more than your recruiter's cattle-call throughput, each and every one of them.
Have some empathy, my dude. Or at least some enlightened self-interest, for someday will be your day in the barrel.
I'll happily give advice, feedback, mock interviews, and other sorts of help on my own time in more appropriate environments. When it's company time, it's just business.
As a hiring manager, you're unlikely to be on the clock. And even if, I am somewhat certain that you could come up with good justifications for giving feedback if anybody asks, which nobody will.
It seems to be a specific disease of middle management to feel the need to demonstrate their "professionalism" by going out of their way to deny their humanity. At Wall Street, they buy ugly but expensive clothes for this purpose. But I guess on the West Coast you only have the Gordon Gecko playbook to fall back on.
I used to work at a branding agency, and it was interesting to see how risk averse middle management was: ideas for product names tend to only be good if they evoke some sort of not entirely pure concept. Think of "Plan B", "Virgin", or "CockroachDB". These would always get shot down by middle management as "unprofessional". Go a level up and people are far more open to be human. I don't know if they are just more self-assured and therefore willing to trust their instincts, or if the selection process for higher management actually works quite well.
Be decent.
You can't expect a business to feed the hungry, cure the sick, and house the poor out of the goodness of their hearts because these are people that spent a couple hours of their day with you. There are more appropriate institutions for charity.
And why are you stanning so hard for a process whose bloodless mind would bleed you dry and kick you to the curb for a nickel? Was Steinbeck really that right?
The answer is that they'll leave negative reviews, tell people to avoid your company or decimate any goodwill your company might have. I have in the past left scathing reviews on Glassdoor and was on some occasions the first one to drop my experience. Because after long projects or a company promising to get back in touch, they decided to instead ghost me or make me do ridiculous tricks for the application process.
If you view something as a business transaction, then you should know one of the worst things you can do in business is spurn the person you're working with.
I naturally left a scathing review for that place, but Glassdoor removed it (of course).