Idiots on the freeway

OK, I give up.

Why do idiots get on the freeway and drive at 20km/h under the speed limit of 100km/h in the fast lane? I cannot figure it out. Yet the same idiot will do 80 in a 60 zone once off the freeway; do their cars have only one speed or something?

If you are an idiot that does this, please leave a comment letting me know why.