It's an extreme lower bound to make a point.

(And, actually, dollar store headphones are surprisingly decent these days. I use them to listen to podcasts in the pool, without worrying too much about whether they get wet.)

An average quality headphones are in the price range of bluetooth headphones. So I don't understand your point.

I couldn't find anything below 10€ with decent sound quality, and it was hard to find something at that price that was good. Moreover, they lasted around 3-6 months for me, while a 25€ Bluetooth headset I bought 3 years ago is still working and the sound is better.