Headphone jacks are easier to use with friends. A few years ago, if a friend was riding with me in the car, I would offer them a chance to plug their phone into the audio system using a 3.5mm cable. Now, most of my friends don't have a phone with the audio jack, and pairing their phone via bluetooth is a small headache that also seems to have a small random chance of failure.

Similarly, I used to keep a "headphone splitter" cable in my laptop back and backpack. If I were listening to something interesting or funny, I could share that with someone, connecting two (or more!) pairs of headphones to one device. I think it may be technically possible to do something similar on the latest bluetooth standards, but even thinking about trying to do it makes me tired.

On a different note, I have an old but nice hifi stereo in my home. It has a few different audio sources, but the one I use the most is my previous smartphone, which sits next to the stereo, permanently connected with a 3.5mm cable. It has no mobile data plan, but it connects to my home's wifi, and I use it to play music from a streaming service and to my media server that holds a collection of ripped CDs. I think it's a great way to extend the usefulness of an elecronic device, but that is only made possible by utilizing widely adopted standards.