Because that is just what we do.
Expressing things as percentages was a late arrival; when until the mid 70s folks had to be able to cope with, and mentally manipulate vulgar fractions.
Expressing things as percentages was a late arrival; when until the mid 70s folks had to be able to cope with, and mentally manipulate vulgar fractions.
It is also likely to be "one in two" rather than "one out of two", in speech "half", "three quarters", "seven eighths" etc is more likely.