A few trivial reasons why they shouldnt be I guess, voids contact with others bowlers, possible OHS issues and could be listening to mental assistance tracks to help their game to gain an advantage, much akin to bowlers using wristguards I suppose.
Few trivial reasons, but I honestly dont see what purpose they serve especially when worn whilst bowling. IMO it is a sh*t look and if bowling is that boring they have to be listening to music instead of talking to other bowlers or concentrating on what they are doing, best idea is to look for another sport to play.
OMG that is beautiful !!!! Love your work