Wed Jan 22, 2020 7:57 pm  
Another origin for the thri-kreen on Oerth

Where did the thri-kreen come from? Well, they are actually descendants of the Vrusk from Star Frontiers. A Vrusk ship was sent to rescue those on the ship that made up the Expedition to the Barrier Peaks craft, but it crashed. The Vrusk are nothing if not adaptable, and the radiation from their ship also mutated them over the generations from having ten limbs to a mere six.

If you consider psionics to be more "sci-fi" then this is a suitable explanation for why the thri-kreen have a tendency towards them.