That’s because UP Studio generates support roofs for overhangs on top of it’s zig-zag pattern giving a smooth flat surface to build overhanging features on.
Cura by default will only run the zip-zag or what ever chosen support pattern, all the way to the underside of the overhang.
I’ve configured Cura on my machine to generate support roofs on top of the support pattern just like UP Studio does so I can achieve the same smooth bottom surface finish.