GEDCOMs can contain source material; the ones exported from Ancestry definitely do (if the Ancestry record has them). Here's the catch: the import process uses the sources to generate a biography with a horrible hash of mangled and duplicated source citations, that is very difficult to follow or edit if you want to change the sources. The more sources you have, the worse the computer-generated bio, and the more effort it takes to clean it up, and the more likely you will make a mistake doing so. If your GEDCOM has no sources, the post-import cleanup is easy, but then why did you need the import? If your GEDCOM has no sources because there are none, why are you creating a profile at all? WikiTree is working on a major upgrade to the GEDCOM process, so another option is to wait for better tools.