Pairing a device is too complex...
Frankly, I found much more funny people walking with large stereo headphones connected to a smartphone...
I use a bluetooth headset every day while driving or even when I have to talk on the phone hands free, and maybe away from the phone. Instead fighting with headset cables, it's far more comfortable - and now there are models that can connect to two phones at once (useful if you have a company phone and a personal one - which I do because I do not want to have my personal data on a company-controlled phone).
Frankly I never understood why Bluetooth headset didn't become much more common - I guess the issue is most people buying a phone - smart or not - can't really use it. Pairing a device is beyond their skills. And after all you have to show off your phone... keeping it in a pocket while speaking using the headset won't do it.