Or the fact that nothing about them even kind of attempts to have a theme. Their most enthusiastic fans also prefer them being an amusement park. They are also the number 1 park, amusement, theme or otherwise in the country that is not open year round.
I think the key to a dark ride is that you are in a vehicle that is led along a desired path and your view is directed in a guided direction to various show scenes ... so as long as a ride does that, it doesn't matter what speed it goes at.