When you think about how common the basic symptoms are, I think it could take quite a while before someone wondered whether it was different from the common cold and went testing.
IMO Its a perfectly reasonable theory that it was spreading slowly through China for months, from some distant province, and it wasn't recognised as a new virus until it arrived somewhere there was the expertise to look at it in the right way.
That would mean that the reason it was found in Wuhan and not anywhere else is just because Wuhan was the first place with people who had the expertise and the interest to investigate and figure out it was new.
Whatever the truth is, that is just as good a theory as any other, and it explains the apparent evidence for the virus appearing a few months earlier in some countries.