The advantage of having numerous diaphragm blades

As you can see above, a large number of blades allows for a more aesthetic background blur. The points of light are rounder and less angular.

Why limit the number of blades?

A small number of blades is easier to manufacture, but that is not the main reason.

A large number of blades also causes the diaphragm to close more slowly.

However, for cameras that allow you to see through the lens, for greater comfort, you will want to see at full aperture for a brighter viewfinder and close the diaphragm only when you release the shutter.

Therefore, in order for the diaphragm to close in time, we will have to limit the number of blades.

Not that important

The number of diaphragm blades ultimately has little impact on image quality.

I have used SLR cameras and therefore lenses with a low number of diaphragm blades to take most of my photos. And I have never rejected any images because of light bubbles that were not perfectly round.