They had a purpose, but swords typically required more materia, time, and skill for y'e old blacksmith to produce in great amounts. Also they required considerable training to be any decent with. Thus they were weapons associated with professional soldiers and the nobility throughout the ages.

For your average peasant or levy soldier that was pressed into the army, giving them swords was highly impractical and expensive. Thus assortments of spears, which were much cheaper, required vastly less time and material to make, and easy to train with, was the weapons of choice almost universally until the advent of firearms.

As I understand it, they were usually carried as sidearms by knights, while peasant infantry that made up the backbone of armies usually carried easier to produce and easier to train on weapons, including (ironically) the war scythe.

This goes on the end of a pole, btw.