How are trails selected for Google Earth?
The exact method for determining if a trail is selected for Google Earth is a carefully guarded secret by Wikiloc (in order to prevent abuse and artificially tweaking trails).
It's a combination of a minimum TrailRank, whether the trail is in an area with few other trails, favorited by other users and also the level of activity of its author among other factors.
In general, to get your trails selected for Google Earth, the same recommendations apply as to increase the TrailRank of your trails.
The routes you upload to wikiloc.com can take up to a week before appearing
You can read the post on the official Google blog.