Issues with migrating off Wikia

"FANDOM", formerly known as Wikia, has suffered from an extremely tarnished reputation as of late. With numerous problematic and controversial changes, such as a forceful migration from "wikia.com" to "fandom.com", the desysopping of a local administrator over local issues that Staff should never have been involved in, and disruptive introduction of Featured Videos, there is great incentive for wikis to migrate off the platform. Numerous wikis, such as the Runescape Wiki, have already left, with many other wikis of various sizes at various stages of trying to leave. While there are certainly many arguments for the migration off Wikia to a different platform, there are still many reasons that prevent most other wikis from being able to make the decision.

Hosting, technicalities, and maintenance
Wikia allows wikis to download database dumps of their content in .xml format. These can be used either as personal backups of wiki content, or to import into a different MediaWiki installation. This is possible because Wikia uses a Creative Commons Attribution-ShareAlike license for most of their wikis, and the license permits reuse of content, even for commercial purposes. It is also possible to simply use Special:Export to export entire page histories and import them into another MediaWiki installation.

The primary issue many wikis have, particularly those in smaller communities, is the issue of hosting. Questions arise as to what wiki hosting services should be used to house the new wiki. If the wiki wishes to continue to use MediaWiki, options like ShoutWiki and Miraheze have their upsides and downsides. ShoutWiki allows for immense freedom with few restrictions on what communities can do technically, but have a limited customer support staff and don't support HTTPS. Miraheze offers good, polished software, but enforce other restrictions, such as a dormancy policy that removes inactive wikis, that may make migration difficult.

Wikis that decide to host the new wiki themselves must contend with many more difficulties. They must have someone on-hand that has the technical expertise to install and maintain an installation of the MediaWiki software, and must be able to maintain the servers and the infrastructure needed to keep the wiki running. They must also deal with spam and DDOS attacks, and have to handle security patches and backups on their own. For a small wiki with few resources to begin with, self-hosting is not an option. Even for established wikis, self-hosting is a challenge if they receive a lot of Internet traffic on a daily basis.

The old wiki continues to haunt
Wikia does not allow communities to close the old wiki down after migration, nor do they allow communities to post links around the old wiki pointing to the new site. One example is the Feed The Beast Wiki, which successfully migrated to a new site, but conflicted with Wikia Staff when they attempted to redirect readers to their new site. This resulted in the blocking and desysopping of two local administrators.

Once a community has migrated off the platform, the old wiki on Wikia will continue to exist, dominating search engine rankings and continuing to draw in readers, while the new wiki may struggle to attract readers even if its editor-base was successfully migrated. Links on other sites will continue to point users to the old wiki unless they have all been individually updated, and if parts of the community choose to remain on the old wiki, communities will be divided between those who wish to stay and those who wish to leave. As such, any new wikis that are created will have to compete quite aggressively in order to have any chance at overtaking the old wiki, if they are at all successful. Wikis created on Wikia

Vendor lock-in
In addition to issues with search engine rankings and Wikia's refusal to redirect the old wiki to the new one, much of Wikia's code was written for use on Wikia only. Examples include the Portable Infoboxes markup, which was designed for use on Wikia only. Infoboxes written using this markup will not work outside of Wikia unless the PortableInfobox extension is also installed. It may be the case that wikis will need to rewrite many of their templates and gadgets in order for them to work on other MediaWiki installations. The things that are most likely to break after a migration are Javascript gadgets and CSS customizations, which may not work on other skins or on newer MediaWiki code without modifications.

Wikia might just come back for you...
On December 12, 2018, Wikia announced that it was "joining forces" with Curse Media—in other words, Wikia had purchased Curse Media from Twitch. Curse Media owned a wiki hosting service for game-oriented wikis called "Gamepedia", which many wikis like the World of Warcraft Wiki had migrated to in response to Wikia's shenanigans. The news of the acquisition shocked the community of Wowpedia, fearing a reintegration into the ecosystem they had attempted to flee. There is no knowing whether other wiki hosting services may sell their services to the highest bidder, which may very well be Wikia. The solution to this issue may very well be self-hosting, which as mentioned above, has its own plethora of issues.

Conclusion
To say "just leave Wikia and make your own wiki!" flippantly in response to criticism over Wikia's controversial changes is improper because there are many reasons as to why migration from the platform is difficult. Both small wikis and big wikis face numerous challenges with migrating off the Wikia ecosystem, and there are many legitimate reasons to stay because of them. In any case, wikis both big and small are left in a trap, where all available options seem equally undesirable.