The MDN site on the other hand is a pure technical reference site, like PHP.net.
Considering that search works by way of matching search phrases to site text, it's not at all surprising that Stack Overflow and W3Schools rank higher than the reference manual sites.
I'm never disappointed.
You can guess the answer for w3schools...
To be fair, a site like w3schools will worry much more about SEO than MDN, but I'm willing to bet that "shows our ads" has a positive impact on site ranking.
Low quality results that display their ads are the ideal scenario for Google:
1 user searches Google, sees some adds
2 user visits low quality site, sees more Google ads
3 user doesn't find useful information, goes back to search
4 repeat
1. Marginally cleaning up low-volume technical search results is not going to get anyone promoted or a stock refresher.
2. Most of the programmers at Google are probably good enough not to have to Google programming questions.
And agreed about w3schools, expert sexchange, etc.
This is the most hilarious concept I've ever heard.