there are two reasons why someone would want this -
1. it's analogue. i know computers can fake analogue, but there is a difference.
2. real time control. not important for everyone, but some people would like to make their kick slowly and smoothly evolve. yes you can fake this with a computer, but i find i can hear the stepping between values with any virtual analogue gear or programs.
bonus reason -
the full jomox drum machine is pretty expensive, especially considering that most people only care about the kick. there's also a lot of new modular analogue gear out there these days, which for live performance is a lot of fun. i like having a bunch of little boxes with knobs that i can patch together in different ways - yes, you can do that with a lot of programs as well, but i'd prefer a physical interface, and gear that isn't pretending to be something it's not.
disclaimer - i like using computers to make music, but i tend to use them to do very digital things, rather than fake an analogue kick or synth. the right tool for the right job.