The amount of energy that I have to devote to perlmonks is highly variable, and therefore I wouldn't want my name listed as an official resource for an entire subject area. Also I suspect that mentoring works best when the mentor and mentee have an established relationship rather than switching with every subject area. (Mentoring in my eyes is distinct from teaching...)

Others may have similar concerns.

Additionally I don't think that popular voting by perlmonks people is a good way to establish expertise. For instance I am often thought to be good at "functional programming". In fact I happened to post some influential articles while integrating together my understanding of how to program using closures. Accidentally I did use some functional techniques, but that was an accident since I didn't know what functional programming was. Furthermore in making up a name for what I was doing I accidentally caused many Perl people to define functional programming somewhat differently than it is understood by the broader programming world.

My "expertise" would not, for instance, be sufficient to be of much assistance to someone who was trying to translate an example program from Haskell into Perl.