rframe pretty much summed it up. As I pointed out before the two main reasons are lack of qualified instructors and effective equipment to teach in.
Unless you plan on becoming a professional test pilot, airshow performer, flying competition aerobatics or teaching stalls & spins there is very little practical reason to learn how to intentionally spin an airplane. Just for the fun of it doesn't seem to matter... So, like the FAA, we focus on prevention. Now here's where it differs. The FAA just wants to talk about it. In reality, there are VERY few pilots who could actually recover from a spin with the FAAs PTS requirements and the procedures outlined for the specific aircraft in the AFM. Most POH/AFMs suffer from a loss in translation between the test pilots notes and the writer. Besides that, if most pilots are taught to completely avoid stalls by timid CFIs and DPEs how are they ever going to deal with the realistic distraction of the spin? Knowing what it takes to stall and spin an airplane from any attitude is what will ultimately prevent stalls and spins. If you never learned how far you can take it how will you know when you get there?
The student is only going to be as confident in the airplane as their teacher. And students can sense when the teacher has some apprehension about the task.
Typical CFI/student interaction:
CFI: Don't do stalls they're dangerous
Student: Why?
CFI: You could enter a spin
Student: Can we do spins?
CFI: No, spins are too dangerous.
Although over-simplified, there is a lot of truth to this interaction. Stalls and spins aren't inherently dangerous under the controlled circumstances. It is the CFI's duty as an educator to understand and provide the controlled environment for the student to learn in. There should not be a single CFI applicant turned CFI who has one iota of apprehension with the practical application of stalls and spins. The CFI should be able to demonstrate instructional knowledge in spin dynamics, and go out and show they understand. Concepts like: Spin axis, mass centralization, yaw/roll coupling, flat spin, blanked control surfaces, sources of yaw, sources of roll, P.A.R.E, aggravation, in-spin aileron, out-spin aileron, gyroscopic precession, application of power, cross-over spin, transition spin... should not be foreign to new CFIs. Believe it or not, once in a while I run across CFIs who still thinks AOA is synonymous with pitch attitude....
The information is out there, here are 3 books that every CFI should own:
http://www.richstowell.com/
"Emergency Maneuver Training"
"Stall/Spin Awareness"
http://www.amazon.com/Stalls-Spins-Safety-Eleanor-Friede/dp/0025816209
"Stalls Spins and Safety"