I was curious how many open profiles there were by Birth country so I created such a list -
https://www.wikitree.com/wiki/Space:Count_of_Profiles_by_Birth_Country
It will probably come as no surprise to anyone that the countries with most profiles are the United States, England, Canada and Australia. It might be more of a surprise that the Netherlands has the next highest count.
The "place" with the 2nd most profiles is actually profiles that lack anything in the birth location field. These are 17.19% of the total (5,396,866 profiles).
The 10th highest count is for profiles with an unknown country (meaning WikiTree+ could not determine the country due to data and formatting). These are 1.66% of the total (519,958 profiles).
Edited to add: I have added a 2nd chart for places above 200,000 locations which includes regions (States/counties/provinces). Virginia, Pennsylvania, and New York have more than the Netherlands.