[ Well, it wasn't very well-known publicly, but... ]

It's for their Trion glands. Have you heard of them? Trion is seen as an extremely valuable resource, or so I understand. Nations are constantly trying to steal from each other -- so a big, juicy population center that can't guard all its citizens is a very tempting target, indeed.

If that's what's happened, and they've kept us alive for this long, I think it would be more advantageous for them to treat us well.