Why does a helicopter has 3 wings not 4 or 5 ?

There are several factors, the main four are;

Rotor diameter and gross weight. That translates to a factor called "disk load" (weight / rotor area). There are ranges of disk loadings that favor X number of blades.

Then there is the blade chord design and its aspect ratio (length / blade area), again there are ranges of lift produced by various chords and aspect ratios. (Chord is the profile shape, and there are hundreds of different ones to select from)

The third major factor is mission, is it a light, medium or heavy? Is it commercial utility or military attack?

And finally, what power is available. More blades need more power.

All this and more are factored into the rotor design, and it is an iterative process, simulating different combinations till the ideal configuration for that specific helicopter design is found.