The fact that you think they don't work is even more revealing...

That depends on your metric of 'work'. By the same metric, buying email lists from spammers also 'works'.

How does getting people to voluntarily sign up to receive emails about a topic that interests them compare AT ALL to buying scraped emails?

You are wrong, and I don't mean to sound insulting but it seems like you are making these comments on theory and not on experience.

I have multiple sites with pop-ups that see outstanding open and click-through rates, it's not even close to the same thing as buying an email list (which doesn't work, as you pointed out).

On what are you basing this on? I know very knowledgeable marketers use them and I can guarantee you that if they were not performing they would have removed them.