If I had to guess? One certain Mad Titan who was on the hunt for a bunch of ancient powerful artifacts almost as ancient and powerful as I am finally got them all and used them to cull half the living beings in the universe.

[ Glancing up at nothing as though reminded of something. ]

...Come to think of it, I think my brother, the Collector, had to have had at least one of them. That's concerning.

Anyway.

[ This is probably the most honest he's been about his situation since he got here. ]

I assume that's actually why I wound up here. It's easily the only way he could have killed me and if you're alive you've got a 50/50 chance of getting caught in it.