[andrewvc]

The reason is that barbers have sharp things and deal with many people. Also lice. There's a very real public health risk if done incorrectly.

[jusben1369]

Proving that there are reasons for some certification is not really an answer though. I think the question is "Does it really take 2 years to get a solid grasp on those things?" (I've noticed several answers with a similar answer not just yours)