I find the population stats a bit bizarre. Why is the percentage of population by country taken into consideration rather than the percentage of people who iden

I find the population stats a bit bizarre. Why is the percentage of population by country taken into consideration rather than the percentage of people who identify as Muslim? For instance, although Muslims are only about 14% of the Indian population, that 14% constitutes almost 11% of Muslims in the whole world. That's the largest number of Muslims in a non-islamic country. However judging solely by the graphic (I didn't see a link to the study), it appears as though Indian Muslims are not represented.