Why are most women so needy in relationship ?

If that's your experience it probably just means you have a "type" you tend to go for over and over again. Because clearly there are more self reliant women out there. They just tend to be objectionable to some guys in other ways (because they have their own lives and don't dote entirely on a guy when they're dating him). So it's a tradeoff you have to make... Women who give you all their time have nothing else going on in life so of course they're clingy. Women with interesting and varied lives don't hang on your every word. So you just have to pick a different kind of woman to date. 

The more insecure a woman is, the more needy she is.  But men can be very needy too .. seen when they fall to hard and fast, but also when they get jealous.

Sociologists say that 97% of all families are dysfunctional, and that means that 97% of us - male or female - grow up with dysfunctional subconscious patterns and some degree of insecurity.  Some people outgrow their issues and stop being insecure .. others don't. But by and large, the younger someone is, the more likely they have emotional problems they haven't fixed yet.