For the same reasons that I like NHRA Stockers. They are allowed only minimal modifications (a pipe, a strap, and a set of dog-bones mostly). They run all stock engine parts, stock frame and swingarm, stock wheelbase, and full street equipment, including DOT-legal tires. I think it helps people to realize how fast these bikes really are.

Here is Ryan Schnitz, running in the old 600cc class about 8 years ago:

http://www.youtube.com/watch?v=I5f_KX1juq4

And here is Vince Woska, running the current 1000cc class:

http://www.youtube.com/watch?v=ZyFHrQRPlkw