Short Reason: Oasisgate.
Slightly Clarified Reason: While newer users will compliment the things they see (mostly because they are unaware of how things used to be), the mechanics behind wikis on wikia are the opposite of user friendly. Wiki editors beware, Oasis is a nightmare. The lack of customization options (or should I say, the removal of them) make creating truly impressive wikis on wikia, impossible. Also, forget about the staff at Wikia listening to any suggestions you or thousands of others may have.
I have two wikis on Wikia and it is a great script with a well-written layout. The skin is ugly, but I don't really care about that. I found Wikia searching for information about Walt Disney World and came across a Disney wiki on Wikia. I love Wikia.
After a move to another host with the layout-change-fiasco, Wikia staff was uncooperative and effectively took over the wiki, refusing to allow the former admins to run it, threatening to ban the former admins, and being generally difficult. The members of this wiki had a horrible experience with Wikia, and now I'm not so keen on Wikia as I once was.
Individual Wiki communities can be either wonderful or horrible.
In the past, there have also been issues with malware hiding in the ads. May not be Wikia's fault, but it was still a problem.
Until the end of 2010, the community that I am part of used Wikia as a place to share information and have contact about our activities. It went relatively well, despite some minor conflicts.
However, near the end of 2010, Wikia decided to force a hideous layout on its users. Since our Wiki used a lot of diffult infoboxes and tables combined with large amounts of text, this hideous layout destroyed many pages.
It was decided that the Wiki should move to a different site. After some detours through other sites, it was decided that some people in the community would pay and build their own website using MediaWiki. This has gone relatively well, but another issue has arisen. Wikia is still in use by some misinformed people who are new to the hobby. When the name of our Wiki is searched for on Google, Wikia is usually the first result. We have tried to inform the new users that our community has moved to its own website, but Wikia has responded by removing the messages arguing with the users who posted them.
At the moment, the Wikia site has no proper moderation whatsoever. Most articles are outdated or ridiculously bad and users hardly ever contact each other. This is the result of Wikia's refusal to let us talk to them properly and, of course, of Wikia's refusal to simply delete the unencyclopædic anarchy that the old Wiki has become.
Forced new and worse features upon every wiki, completely undoing hours of work, ignoring community's intentions, forcing many wiki users to move their wikis to other hosting sites and disallowing wiki owners to state they had moved
A bloated and pompous site to begin with, things got worse when they let Merrystar join the "Helpers." This rogue started inflicting sitewide bans on users for NO REASON, then making it near-impossible to complain to other staff about her actions. And when I complained anyway, no sooner did I go back to check the site than I was infected with XP Total Security 2011, a rogue anti-spyware program. Now, my laptop won't open Firefox or other applications. The custom desktop features don't work either.
I recommend this farm to nobody. Holier-Than-Thou, vindictive, and Symantec Anti-Virus is powerless against the bugs you might be hit with going here.