Not much reason. Was hoping to save ppl some coin, but not sure how much is actually saved this way. Think it's about $3 in plastic to print. Could easily be adapted to various ball sizes (haven't tried, but script is quite flexible). Can also tweak the height to play with how much ball is exposed above your panel. Easy to connect this to USB via a simple micro-controller or any arcade trackball to usb encoder. Could use a cheap raspberry pi pico or arduino or whatever and find relevant code online to do this. I have a pico doing this and keyboard combined, nkro, and very inexpensive.
The encoder wheels, however, let you tune the performance, getting a finer grained input from the device with more spokes, and vice-versa. Should work with any trackball of this type (happ, betson, ggg, ultimarc, etc)
Did some atari volcano buttons a while back, so I guess this is just the next installment in arcade parts.