If half of your five year olds are “not ready” for kindergarten, the problem is with either A) your instrument for measuring readiness and/or B) your expectations for what “readiness” looks like.
It cannot be said often enough–if you discover that a huge percentage of five year olds are not ready for your kindergarten program, that is an indictment of your program, not of the five year olds, their parents, their teachers, or their breakfast cereal.