Because it does'nt show the distribution of money
whether it is equal or not

EX:            1st person 2nd person 3rd person 4th person  per capita
country A  :2500          2000          2200         2300             9000
country B  :1000          1000          1500         5500             9000

in the above case country A all the people get equal distribution of money,and in country B only one person gets more money

Hence we can say that per capita income doesn't show the distribution of money of the country,whether it is equal or unequal.