Some pages are pretty good, and poor quality content gets downvoted and eventually deleted anyway. To take an example if you search for "php mysql" on Google, the top result is a w3school page full of ads with little content.

The Documentation page for this in comparison is helpful and gives a good overview (with more and more detailed topics as you scroll down): https://stackoverflow.com/documentation/php/2784/php-mysqli

But again if it doesn't show up in search results it doesn't matter. That also means there's less of an incentive to improve the content since nobody will read it.