Not quite. It was mainly because they're entirely independent. As you know, it's explained that every human being has an AT field, and an AT field is what separates us from one another. Thus, the more independent you are, the stronger a personal AT field you have. (One of the reasons why Gendo abandons Shinji)
The only real use for that is that you'll have a higher sync ratio when piloting Eva.
The secondary reason is that each pilot has individual ties to NERV or Seele, somehow.
Asuka had ties with her mother at NERV, she inspired to be an Eva pilot since childhood.
Rei with Gendo
Shinji with his mom and dad
Kaworu with Seele
Third reasons are souls.