Because it's not active. It's resolved, archived, done. Searching such should be done explicitly, not implicitly; compare GMail.
See http://wiki.bestpractical.com/view/SimpleSearchIncludeResolved -- Cambridge Energy Alliance: Save money. Save the planet. Discover RT's hidden secrets with RT Essentials from O'Reilly Media. Buy a copy at http://rtbook.bestpractical.com
