Countries may come and go, be founded and perish but cultures usually tend to stick around for a long long time or even permanently. This is why a country, especially younger ones, could have a culture that has a different name than the country, especially if it was formerly part of a bigger country that broke apart but the culture is still present. A country can also have multiple cultures within its borders, especially big ones or those that conquered others and integrated the foreign culture. The culture is an important identity for most people.
There are also culture groups that contain different cultures that share a mutual origin. Cultures that are part of the same group are still different but often have similarities and sometimes a feeling of kinship - think of it like how Portugal and Spain in our world are both part of the Iberian culture group but still different (plus, there are different cultures within Spain like Galician and Catalonian).
The entries here are cultural groups and it is easily possible to add more. Each continent also has a cultural map that shows where cultures can be found (you will have to request an edit if you add cultures). If you only want to add cultures to an existing culture group just comment on it and ask the creator. It is also possible that a country has a singular culture that is not part of a culture group and just its own.
You should add more info to cultures although that is just optional. However, I would say that naming conventions are important which often differ from culture to culture. Naming conventions are basically cultural "rules" regarding how to name children and what kind of last names (if they have any) people have.