How ear buds make you a more unfriendly person
Almost everyone at the gym has stuff going into their ears through some form of wireless device. For many, they go together - exercise and music. I bet there are situations where people would skip their workout sessions because they've run out of charge.
I don't like wearing things in my ears at the gym. They could accidentally fall out, the music rhythm might not synchronise with the reps you are doing and you could end up wasting time choosing tracks. Also, you miss out on talking to others (given they aren't listening too).
But that's just me.
Socialising is kinda part of the workout too. Intellectual and conversational exercise. A healthy lifestyle involves both engaging your core and your neighbours.
With your ears plugged, you're pretty much sending a sign to others to be alone, undisturbed and isolated. Putting it bluntly, your earphones are a physical barrier to you engaging with the outside world. When you put them on, you send a signal that you want to be ignored. As a result, others would do the same. Soon you'd have a room full of very quiet humans.
While there are introverts who truly feel better left by themselves, I believe most people aren't that way - they just prefer listening to tunes. But if it becomes the norm, you might end up programming yourself to listen to music instead of having a meaningful dialogue with a friend, old or new.
I keep myself open - at the gym, or anywhere else. There are opportunities abound for sharing ideas, information and inspiration. You get to learn tips, or even impart your knowledge to help someone have a better day. Humans are social creatures and so what if you don't get to work on your traps? You can practice your chats!