To reduce time, as simple as it sounds, but that's the only reason. Creating fluid animations takes time, rendering them takes even more time. The animtaion preview in daz isn't really good, so most of the time you only see if the animation is good after it is rendered, and the chances that it sux is really high, so I tried to minimize the risk while also doing the best I can to make them look good and fluid.
I posted it before, but I actually wanted to include different camera angles for the animations, but it simply takes too much time, if I'd done that, I would still be a month or two away from a release.
To give you an example: Katherine has two animations for each gender, one animation has 60 frames = 60 render, only rendering one of these took 15 hours, but that's just the rendering, setting up the scene, posing each frame, corrections etc, take a lot of time as well.
Each of the Ellie animations has 360 frames, and they are way more complex (and still look simple), so we are talking about weeks here.