It's a mechanical movement regulated by quartz. In a traditional mechanical movement, the escapement prevents the main spring from unwinding all at once. It is done with a fork which ticks at a certain rate governed by the balance wheel. In a Spring Drive movement, the escapement is replaced with an electromagnetic "brake" governed by a quartz crystal. So it still has many of the characteristics of a mechanical watch: it's still powered entirely by a main spring which can be wound or automatically wound by your body movements, it needs regular maintenance like other mechanical watches, and it isn't as durable as most quartz-only watches.
That's true but it's still driven by a spring and mainly mechanical. I understand people who don't like it, but I also see it as a reasonable tradeoff and find them just as fascinating as purely mechanical models. In the end people wear them for the same reasons.