It's been a while since I have provided an up-to-date list of the different countries with the most members without a stake. Below is a list of the top 20 countries with the most members and as of yet do not have a stake.
4. Sierra Leone
7. Cape Verde
13. Marshall Islands
Here are some interesting trends. If I were to make this list four years ago, there would only be four countries with over 6,000 members on this list and now there are eight. At the end of the year 2000 only two countries had over 6,000 members without a stake: Russia and Ukraine. Why haven't these countries had stakes organized in them yet?
One of the reasons why is that inactivity and member involvement in leadership has been a problem in some. Stakes take on great responsibilities with sending out missionaries, organization and temple work and require many priesthood holders who are willing and dedicated to take upon these obligations. Of course all of these countries have such leaders and members in them, but they have not been in a large enough quantity and concentrated into a small enough geographical area for the creation of a stake as of yet.
This leads into geography. Members in Russia are scattered throughout what is the largest country in the world. Although there are areas where members are concentrated, there still has been no stake organized. Most members live in the cities of St. Petersburg, Moscow, and Saratov. Other countries have a similar situation like Vanuatu and Malaysia.
Many of these 20 countries are close to having stakes organized in them soon. We have seen great growth in membership in areas where we have never had members of the Church before in the past 10 years. We had a similar situation 20 years ago where several countries had close to 10,000 members before the first stake was organized (like Ghana and Nigeria).