ABS is some great plastic. Non-toxic, reasonably sturdy and impact resistant, lightweight, colorful and can be made glossy or can be textured, hits tight tolerances, cheap, etc.
If you look around your home, you’ll find ABS used all over the place. And who doesn’t like Legos?
For keyboard buttons, I think PBT often makes a nicer sound. But ABS is also fine. The thickness of the plastic also has a big effect on sound.