For some, it is the ability to customize things the way they want. For others, it is the ability to put cutting edge (and sometimes unstable) future revisions on the phone... to get features not yet available to the public at large... for others it is the challenge.
Unlike the iPhone, rooting the Droid isn't so much a need (since you can install anything you want already), as much as a want... it is a geek thing, it is a challenge.
After countless OS leaks, installs, Shrink-A-OS uses, custom OSes, hybrids, etc.... all with my BB Storm I won't give in to the desire to root and play with my Droid.... had my own personal intervention.... no relapse... lol