Perhaps it is important for them to maintain an aura of neutrality and cold calculation. Though if we are supposing that Google is intentionally crippling it's algorithm, would it be so much to suppose that they would just clandestinely run the spam sites themselves to eliminate the middle-man? Though perhaps the cost of secretly doing it themselves is higher than the AdSense payments made to the sites.
This all assumes that Google's reputation remains untarnished by merely linking to spam rather than filling their own site with spam, but I don't think that's quite the case. Google's reputation is intricately tied up with the quality of the results it gives.
I am not suggesting that Google intentionally cripples its algorithms, just that it doesn't rush to "fix" something you or I might consider a problem.
Google's reputation is intricately tied up with the quality of the results it gives.
I think the problem here is the question of whether an adsense-adorned page with scraped content is judged "low quality" by the people doing the search.
I'm no expert in other domains, but judging by the "I CAN HAZ CODES" programmers out there, if they type a programming question into Google and they get a page with scraped content from StackOverflow, will they care?
My guess is that if the scraped content has the answer, they're happy. They aren't interested in doing more research, looking the author's SO reputation, or anything else. They get their answer, and maybe they click an AdSense link if it catches their eye.
You're right, it does depend on people's perception of quality.
I can only recall being frustrated with the scraper sites when they don't have the answer I need, because when I go back to the Google results and try another page I find that they have the exact same scraped content. Out of the first ten or twenty results there are only a few unique pieces of content.
Perhaps if Google eliminated redundancy from their results I'd never even notice whether the content was scraped or not.
I think this may be a big part of the reason why Google employees seem to coyly suggest 'by our numbers these crap results are making people happy' whenever this issue comes up. For a lot of low-literacy users, these results are fine, and as good as they've ever received from Google.
This all assumes that Google's reputation remains untarnished by merely linking to spam rather than filling their own site with spam, but I don't think that's quite the case. Google's reputation is intricately tied up with the quality of the results it gives.