The whole list of world flags available is a representation of all the nations recognized by the global community as existing and able to exercise their political and sovereign powers. While some nations are more developed than others, so do their popularity of being recognized by other people from other nations. Their respective flags are the mere things which get to be identified outright at any given time.
So in the case of popularity of world flags, many would think what the most popular flag should be. Political power, international influence, and the exposure of globally changing things and issues are some of the most common factors which contribute to the popularity of their respective flag. Some would attribute the historical influence of a nation with the rest of the world.
For instance, the American flag may be one of the most popular flags in the world mainly because of their international deals and influence, as well as presence over so many countries. Their operations and economic deals with other countries make them known to the locals of another nation.
Thanks to the internet, the image of world flags are easily accessed and made clear to be associated with the respective country. Even grade school students can now easily know and acknowledge countries and their flags. Popularity of these world flags are simply access to peoples knowledge.
Even if the times and the political arena have caused some of the flags to get modified, their basic colors and main theme are still represented for others to know.