Generally speaking ADs don’t allow comments. Have an example or reasoning why this would make sense?

Some sites do, reddit and twitter for example. Can be useful

Thanks, wasn’t aware either of them intentionally linked ADs to public comment threads.

Have any notable examples?

Comments are usually disabled on Reddit ads. YouTube banner ads for YouTube videos have comments, and it's always hilarious reading them.

for users: How about "I tried it, I like it" or "this product gave me warts", both things it could be useful to know.

for makers of products HN people like: Comments could draw more attention to the product, more clicks, more sales.

for makers of products HN people don't like: No, can't think of a reason why allowing comments on ads would make sense.

The ads are job ads, not product ads. All of your criticisms don't really apply here. I say this as a person who doesn't like them and rather wishes they weren't here.

Nothing stopping any user from creating posts related to an aspect of the content on any of those ADs, but it’s obvious allowing comments for ADs would potentially cause unneeded overhead for the advertiser; clearly if any YC advertisers want to post on HN, they’re free to do so within the guidelines on HN.

HN doesn’t block negative posts about YC companies.