Most of the information at the Traveller Wiki is used by permission from the author and used under license from Far Future Enterprises. This is clearly stated on the pages of the Traveller Wiki.
Since these two licensing requirements don’t match, the contributing users of the Traveller Wiki have decided that they need to move. They have probably been pushed a bit by authors and by Far Future Enterprises that don’t want anyone to say that their stuff is under a Creative Commons licence.
Since Wikia claim that everything at the Traveller Wiki is under a Creative Commons licence (CC BY-SA 3.0), (which it isn’t) this had led to that content from the Traveller Wiki is published in books. Have a look at this one described at Google Books. (I will not link to any of the sites that actually sell this.) Books LLC (a.k.a. General Books and other names) that use this content are claiming that they may do so since everything at Wikia is under a Creative Commons licence. But they haven’t checked or if they have they didn’t care.
In my opinion it isn’t enough (at least not for a commercial company) to use material from the web that someone has posted under some sort of free license. You always have to double-check. Just because someone post something, it doesn’t mean it is free to use. The one who post something that they don’t own (or otherwise may post) may just be a teenager who wants to feel cool when getting lots of likes (at Facebook). It could also be that the person posting hasn’t understood the terms of the site to which the post is made.
I am the author of some of the information that has been posted at the Traveller Wiki. (I have not posted anything myself.) If a lawyer in the U.S. wants to help me sue Books LLC for free we can split the indemnity they have to pay. There are other authors that have a lot more of their writings at the Traveller Wiki.
The business model of Wikia is quite clear. Trick the fan-base of nerdy stuff (gaming, manga, science-fiction, fantasy, vampires etc.) to post at Wikia. Then, present their posts together with lots of ads. Then I suspect that they are in cahoots with Books LLC and share the profits (from the suckers that buy these books).
One strange thing about the move is that Wikia is demanding that no pages are deleted even though Wikia knows that these pages are not using a Creative Commons licence. This only means that Wikia and their accomplices are planning to continue their crimes.
A call to all fans (of something) that has a wiki at Wikia. Move!
A call to all content owners being ripped of by Wikia or Books LLC. Sue!
At the Anti-Wikia Alliance, you can get help with your move from Wikia.
Update: The Traveller Wiki has now moved.
Update 2: Now it has moved again.