So how do you extract "Heart of the Wells" from rogue exiles exactly?

I've got one to drop exactly once. Since then about a dozen rogue exiles have died next to an active abyss, and nothing ever happens.

I've tried googling it. I've looked up a wiki. Well it says nothing at all on how to aquire it on the wiki page, and I'm flooded with garbage spam adds in google, written by AI and devoid of any information.

So clearly dragging an exile to an abyss and killing him doesn't do the trick for me, what am I missing?

Hello there maybe you already found the answer by now, but from what I've been able to find, the Rogue Exile has to naturally spawn within the Abyss crack so dragging/kiting it won't work.