Board Thread:Support Requests - Getting Technical/@comment-24.138.103.226-20150123055753/@comment-1038387-20150123100246

Memory-Alpha was a separate site before it was taken over by Wikia, and part of the deal was probably keeping their old url. That's a rare, rare case.

You can create your own wiki on your own website with the wiki software of your choice (MediaWiki, PMWiki, whatever you wany), it just wouldn't be run by Wikia.