There are more passive people than aggressive ones, and far more conventional-minded people than independent-minded ones.
So the passively conventional-minded are the largest group, and the aggressively independent-minded the smallest.
To be a successful scientist, for example, it's not enough just to be right.
You have to be right when everyone else is wrong.
Conventional-minded people can't do that.
For similar reasons, all successful startup CEOs are not merely independent-minded, but aggressively so.