Why? Because even though they exist, you can neither determine who they really are nor accurately find them efficiently. They are a profile of influence, and that is not a demographic you can target. It is a collection of intangible qualities that makes them an authority.

Scenario: The Web 2.0 conversation about targeting technical influencers
Me: So, how is your Web 2.0 company going to succeed in this very competitive marketplace?
Them: Well Sean, we're going to target the "technical influencer" in our marketing programs. The model we have here shows our growth with that strategy. Once you do that, then word of mouth will facilitate adoption of our product.

Me: So how are you going to "target" them?
Them: I'm sorry Sean, maybe you didn't understand. We are going to create programs that target the "Technical Influencer." That's how Google attained its market dominance.

Me: Uh... yeah, so who is the "technical influencer?"
Them: Oh, ok, yes, yes. They are the people who you go to when you have a computer question, technical question, want to know about that "new" hot site. They seem to have a pulse on the technology, and people listen to them. They are not the "nerds" who just code in the corner, they are the "geeks" that can both spout the acronyms and communicate that knowledge and benefits to laymen.

Me: Uh, yeah. I know they exist, and what they are, but HOW are you going to "target" them?
Them: Uh, I don't think I understand the question.
 
A profile of influence is not a demographic target
The worst part about the above conversation is that someone else probably gave them money based on that idiotic plan. Look, these "technical influencers" exist, but theirs is a profile based on knowledge and influence, not the demographics that define them. They are the one person in their clique who is the influencer, but they look like every other member of the group they are influencing.

I view myself as one, and many of the people reading this article are others. We are the people who are helping shape and define the internet. Is there an approximate age range? Yes. Do they skew male? Yes. Are they mainly urban? Yes. Do they read blogs? Yes. It's fairly easy to create a nice demographic profile, but that does nothing to target them.
 
Understand the implications of defining a profile of influence. You have to have a medium and tactic that will reach your target. Otherwise, defining them is just a creative exercise that does your brand no good.