Who exactly said this? I'd like to see the source of this quote if you don't mind. Was this a private message?

If theymos really said this, it is easy to guess his reasoning. You don't need to ask him.

1- Staff endorsing mixers might get the forum in trouble.
2- Mixers can't guarantee your privacy even though they say they do. That's possibly false advertisement.

We (staff) were asked to stop advertising mixing services.

As for gambling services, then that's simply because of my religious beliefs.