I'm no expert on the "why's" of most things. So, what follows is a culmination of experience, a lot of therapy, continuing self-awareness, and a personal realization of what meditation IS.
Continuing self-awareness because self-awareness is not a one-and-done deal. It evolves.
My experience is that people who have little self-awareness - not just of themselves but of how what they do and say effects others, have a hard time with meditation. Also, those who have to be in control of everyone and everything have difficulty.
First of all, my definition of meditation:
An environment where you feel comfortable, safe, and secure.
A little pocket in your mind where you can do or think what you need to - to find peace.
A place to focus if you want to, dance around if you want to, kick over furniture if you want to, sit and stare, or just be in your particular calm zone.
A place where it's safe to ask for guidance
A place to listen
One of the things I've learned is that you can and should define your own meditation process. My class guides you to make that realization so you can carry it forward and make it your own.