I started using them recently but I already wasn't talking to strangers for a long time before that.

I suspect the constant stimulation suppresses the default-mode network, the idle wandering your mind normally experiences when you're doing nothing.

Before that, I'd sometimes hold my phone up to my ear to listen to a podcast (even on the subway at minimum volume) but it was awkward so not ubiquitous. I think buying a paid of wireless earbuds was one of those decisions that made my life subtly worse overall, like eating a whole tub of ice cream.