Wikitree does not "autopopulate" family trees, like Ancestry and my heritage do. The task of autopopulation usually leads to duplicate profiles for people.
Wikitree is trying to build one global family tree where every person gets one profile only, which is accurately sourced.
So when you upload a Gedcom, you must compare every name on your Gedcom with every name shown as a possible duplicate, in order to not create a new duplicate.
This does take time to do but it is a necessary step.