That is not a very large percentage of the population of Athens.
Historians estimate that several hundred thousand people populated Athens.
Of the remaining half, the vast majority were women, children, craftsmen, freedmen, etc., all of whom were barred from the democratic process. In the final reckoning, only a few thousand males actually qualified to vote. True, this system was more advanced than anything else at the time, and it served as the basis of modern democracy. But it was far from our modern democratic vision of the perfectly egalitarian system of one person, one vote, and equal justice for all. Even the greatest Greek thinkers did not consider the latter approach logical.