As Dave says, you need to "match" or "reject" every suggested match in the Gedcom before you will be shown "ADD" buttons that will allow you to add profiles not already in WikiTree.
For best results in using Gedcompare, after you have taken care of all of those yellow-highlighted suggested matches, go to the entry for someone who is in your Gedcom and is matched to a WikiTree profile, and do a COMPARE. The Compare screen will show that person's immediate family in your Gedcom, lined up against any matching profiles in WikiTree. For people who don't have a match, you will see an ADD button. Work systematically through the family members on that compare screen. Add parents before you add siblings, and add spouses before you add children. When you are done with that screen, open a new Compare screen with another person (maybe a person you just added) as the "home" person. Wash, rinse, and repeat...