If you mean why were 1, 2 and 5 specifically chosen as the divider ratio numbers, I would guess because they are easy number to work with. When reading the graticule on the sceen it is easy to do the mental arithmetic when those numbers are used. Technically there is no reason why other divisors couldn't be used instead but it would be less convenient. Some very old oscilloscopes used x1, x10, x100 but the large jumps made it difficult to find a good compromise between scaling to fit the screen and accuracy of reading against the graticule.
Brian.