It's because people just starting to learn about them and when they hear Arduino they think:
- oh, I need to do programming, I do not have time nor the skills
- with all those modules soldered together it's never going to fit into a hilt
But reality is quite different.
You do not need to have any programming skills, there are excellent open source saber software capable of more than entry or mid range commercial saber boards can offer, like the
GitHub - Protonerd/FX-SaberOS: System code for Arduino based Lightsaber replicasAnd there are tiny Arduino compatible DIYino
www.protowerkstatt.com boards you can fit even into the tightest of hilts.
Installers of course do not want to mess around with software, that is not their focus area. On the other hand side a programmable board like the DIYino Prime or Stardust would allow them to have custom effects and settings which they could use to add value and uniqueness to their builds, differentiating their products further from the competitors.