So where DO they even come from?

I think it gives you extra copies when you buy it. That's why people end with stuff to give.

More than likely from HERE

Bundles mostly. Here's an active one

Original copy ---> 2 gift copies after redemption ---> one more gift copy each after redemption

This is why every copy spawns a total of five copies of the game, and why it just keeps multiplying. Many months ago, there was a free giveaway of I think 10,000 copies, each of which spawned copies like this, so that didn't help matters any.

I think there was an event where they were giving out thousands (100 thousand I think) The Ship keys and each key gives 2 gifts