Keith, at times of utmost concentration, there is a switch to turn music off..
Some of us are not working on racebikes all the time...
pretty sure those guys you mentioned dont want anyone dropping in, especially if music is too distracting to them..
I have been in shops where music is not allowed and it is not always by choice of all involved..
Some of us build custom parts and bikes, and unless you are total TECHNOGEeeK, this usually involves time spent staring at a bike, moving around it, looking at it different ways, laying underneath it.. holding or taping parts onto it...etc..etc..... and often done with tunes in the background..
..JMO..