It was kind of fun to watch them run up and down their rails. And when you pushed the call button, you could just look up or down, see the elevator moving towards you, and have a sense of when it was going to get to you.
No stress, much fun.
Compare this to the common experience with most elevators. You press the button, and wait, and press it again, and wait. And wonder when it was going to come. And wonder. You have no idea that it's there, until it finally dings, and the doors open.
Even if the wait was no more than it was with the visible elevators, the stress level is much higher.
This principle generalizes. If you are building something, any if there is ever a chance that someone will have to wait for it, or puts their fate in it's hands, make it as transparent as possible. If you don't, I'm going to (correctly) think you either don't have any pride in your work, or you are wanting to lie to your users. Or both.
People need to see how things work, even if they can't do anything more than press the "call elevator" button.