I had to quit doing so, because I discovered that it didn't just exclude listed domains, but performed a totally different search. Locations or local results were largely missing, when I excluded some domains.

That's curious, please expand on this. Do you really mean it performed a search for different thing? If so - have you figured how it differed?

Or did it just have to perform a non-cached search and thus not only excluded said domains, but could also reorder the other results based on the current relevance, rather than cached relevance from the past that is being served to everyone else who doesn't exclude said domains?

When I search for “pizza hut”, I get: the info panel that shows Wikipedia intro and company social media profiles on the right, locations results and integrated map view as the second result. When I search for “pizza hut -site:pinterest.com”, I get none of those. In addition, results are listed in a different order.

PS: I'm blocking all ads.

I have a strong memory that Quora used to be quite good, and then was suddenly horrendous. Is this just me?

Not just you, it used to have solely high quality Q&A...then the yahoo answers folks migrated over

if this was the main cause, the expected result would be lots of highly-upvoted bad answers, as opposed to lots of scarcely-upvoted bad answers that somehow rank highly in Google searches

Quora used to be good but then they had to try to make revenue

Quora has plenty of potential for making consistent profit without whoring itself out, but consistent profit isn't enough in the post-Freedman world that we live in

They started monetizing it by paying people to write answers, so it's now full of blogspam.

Quora was excellent for SEO, so brands and companies started using Quora answers to pump their own products and services. It's completely useless now.

I wouldn't say that's the problem I've observed. around 2015 or so I remember consistent useful Quora answers from Quora. it was Yahoo answers but better because people could justify with qualifications. I actually had an account briefly

then I'm not exactly sure when, but definitely by 2018, every answer I ever see on Google is either incorrect, answering the wrong question, or in broken English. commonly all three at once

I don't recall ever seeing a product placement, although admittedly I stopped clicking a long time ago

my educated guess is that due to some likely seo-related concern they deleted/archived/unlisted their old good quality answers in favour of newer more seo-friendly answers

it may not even be their fault, it's possible that Google's algorithm just doesn't drag up older answers from their website, but given my experience with the decision-making in the brief time I was a user there (e.g. removing the ability to add a description to questions) I suspect not

Pinterest uses different domains for every country so you'd need to add around a dozen qualifiers to get the big ones excluded.

same here