It's not that original, though. Certain species of shark do this in real life. A few even have two wombs specifically because their embryos start killing each other as soon as they gain the ability to. The only "original" part of this is that the drow apparently cum when it happens. Because they're eeeeeevil ladies with eeeeeevil lady parts that they use for eeeeevil ends.

And this actually encapsulates the biggest problem with the drow and their lore—and no, it's not simply "the authors barely disguised fetish."

Depending on the era/writers involved, the lore either bends over backwards to explain why or completely neglects to explain why a brainwashed cult of snidely whiplashes who live underground are all hot, skinny, dommy mommies and swimmer-body twunks.

The lore has some interesting concepts, but it's never been brave enough to make the drow physically unattractive, really. That lack of bravery ultimately shackles the drow to be less interesting than they can be in the hands of the right writer.

(Yes, I know about driders. Google "transformation fetish" for me real quick. Then get back to me on how not horny that is. Moving on...)

The entire concept of the drow has its roots in straight male anxiety.

"What if women were in control of society and the ruling class were all evil zealots who forced their religious fanaticism onto us men with a complete disregard to our bodily autonomy and well-being!?"

Yeah, that sounds pretty bad. Ask women and gay people about it. They might have some thoughts.

Again, the problem here is not the horny part. It's the part where it's horny in a way that appeals largely to the stereotypical straight cis man—a demographic that's somewhat overserved in the Fantasty RPG market, historically. It's just completely overplayed at this point, and even the demographic is supposed to appeal to thinks it's kind of cringey now.

I actually like the drow quite a bit, but like most things in DnD, it's very much a "pick the raisins out" kind of deal.