The My Home redirect is a special kind of redirect. It causes the url of the site without any subdirectories i.e. wikiname.wikia.com to redirect to Special:MyHome rather than the Main Page.
How to disableEdit
The redirect can be disabled by individual users in their own preferences. Under the "Misc" tab, there is a checkbox labelled "Disable my redirect to My Home".
There is no simple way of disabling the redirect by default on a wiki.