http://www.ChristianStandard.com/articledisplay.asp?id=213 Here is an excellent article suggesting why some people won't participate in the Arise Groups. It explains what makes Introverts tick.
I've often wondered why certain people weren't participating. Some are on the Spiritual Development Committee. Shouldn't they be involved in the parish's faith sharing groups? Or why members of the parish councils aren't involved in parish activities? The perception is that they don't support the groups or events.
This article will offer some understanding of personality types.