It's not about if the music is helping the bowler, it's about the devices themselves.
They can be dropped/falloff while your bowling, which can cause problems for you and/or other bowlers. Like tripping, delay of game while it's being retrieved (especially if it falls on the lane past the foul line, you have to stop and get permission to retrieve it yourself if you don't it's a foul or get someone to get it for you) from your lane or someone else's.
If your playing it very loud (and there are people that play the music so loud you can here it coming from their earbuds) it could distract other bowlers.
Here's a example of the rule from the 2019 USBC OPEN CHAMPIONSHIPS
Rule 9. ETIQUETTE
A. DEVICES/HEADPHONES - The use of an artificial device to listen to music or a broadcast is prohibited during competition.
http://usbcongress.http.internapcdn....lesForWeb3.pdf
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