The best reason I can see for the small GEDCOM import is so that members can see what their profiles will look like once they have been translated to WikiTree's format. This is regardless of how comfortable members are with WikiTree itself.
I imported a GEDCOM in December 2014, after I had been an arborist for almost a year, and was still shocked at the results.
Manual uploads are often easier to handle than GEDCOMs because:
1. It is usually faster to enter a source by hand than to edit a morass of tags and incomprehensible sentences, especially when this morass is repeated in its entirety several times as evidence for multiple facts on the profile.
2. With manual data entry, members can ensure that connections between family members remain intact. (They are broken with every skipped match on a GEDCOM import.)
3. Even with a GEDCOM import, members are expected to review and edit every new profile.