jointhefediverse.net seems to be a commonly linked resource for directing people to join the Fediverse.
Curiously, it does not list Lemmy under the list of Reddit alternatives. Their GitHub README explains why.
Previous relevant discussion: https://lemmy.ml/post/78808
How was it default? I’ve been here for years and in all that time, it was never default. It was one of the most popular, and the most widely shared, but that’s not the same at all.