The same exact mechanism (and the parent already alluded to it in his comment: "Janette has the same problem while learning about X so she takes his code, makes a few changes and puts it on her blog").

Non experts look for tutorials,

They chance upon tutorials by non-experts

They don't know enough to tell they're junk

They use the code, link to, and suggest those tutorials to others

Those tutorials are getting higher ranks, attracting even more non-experts