A reason for not doing that is that it looks ugly to show multiple options for the same country.

Another is that that can be confusing. Suppose I want to enter a country whose spelling/native name I am not sure of, and after a few characters, four options remain, three of which are correct, but I do not know that. That can cause a needless google to find out, say, the difference between Liberia, Libya, and Libië.