Question

Why are strings of lower tones (frequencies) thicker or heavier than strings of higher tones?

Answer 1

The strings have different thickness or frequencies because of the need to maintain a balanced and even tension when being used. Having different thicknesses between the strings allows the guitarist, for the sake of it, to tune their strings accordingly and generate a desirable output.

With that being said, thicker strings would allow to have a much lower tune whilst keeping a balanced tension between.

hope this helped...