These folks capture the attention of the unaware. Because if you're in touch with reality through any means, you just like you(op) realise what a scam it is. Like all you do is teach how to mug-up for interviews. No one is bothered about teaching the art of writing code that performs well. No one is teaching how to think like an engineer.
Also, I don't think this is bad for engineering community as a whole. For all of human history people have been running such scams. I think one con is that this pushes a lot of uninterested individuals in the trade and that makes for a less wonderful work experience