Why would they do that though? Why would they show you a low quality result if there was a better one available? I have pondered some of these sites as well. I think the answer is that they are actually helpful to some people.
Businesses are profit seeking entities run by human beings who tend to prefer conservation of energy. If a business goal can be met with X effort, X+1 effort is a waste and the resources can be directed elsewhere or kept as profit.
I don't think they track 'quality' they just see people clicking and use that as a proxy for 'quality'. (Quoted because what does quality even mean?)
I seem to recall reading that they (used to?) track abandonment of the search results page as a successful answer to your question from the embedded page snippets or info boxes. So if you get a search result page that's complete garbage and just give up, they increase the ranking of those sites.