making it impossible to divide by three?

30.00 meters divided by three is 10.00 meters

Kilogram divided by 3 is 0.33 or 3.3333333 etc or 3 decimeters, 3 centimeters, 3 millimeters etc depending on the level of accuracy desired.

1 pound divided by three requires converting remainders to ounces, then to fractions of ounces. etc etc.
5 and 1/3 ounces.

adding decimal fractions and putting the decimal point where the unit is so much easier.

do this in your head

express 1 x 10 to the fourth meters in kilometers.
now express 1 x 10 to the fourth yards in miles.