I already responded to this point above, in a different post. I made the very point you did. A lot of technologies have come and gone. And yet, the 3.5 mm jack has stuck around since the 1950s, from the transistor radio, to the Walkman, to laptops and MP3 players, and now cell phones. So the point is, something that has persisted through so many radical technological changes might have something more going for it than people give it credit for.
I would argue that with the 3.5 mm jack what it has going for it is elegant simplicity and quality. Bluetooth actually adds complexity (chargers, the wires on the chargers, batteries that will wear out, pairing and troubleshooting failed pairing, incompatibility with millions of legacy devices, additional cost) and bluetooth lowers audio quality. Bluetooth essentially trades the convenience of not having a wire in one place, for a whole host of inconveniences (and wires!) elsewhere and degraded quality.
You are making the bad assumption that everything new is better. That's not always true. You are also making the bad assumption that when people complain about a change it is always because they are "stuck in their ways." This is also not always true. Some people are more clear thinking and insightful than others (but it's easy to be glib and dismiss them as "stuck in their ways"). Indeed, such vast generalizations found in the assumptions you make are simply bad thinking, since nothing always applies in the same way in every instance.
So just because people stopped using dial phones or typewriters does not mean that dropping the 3.5 mm jack is a good idea. Some new things are improvements and others are not.
(As an aside, I will also point out that we still use the exact same keyboard configuration that was invented for the typewriter. So we may not have moved on from the typewriter as much as you imagine. QWERTY has been around since 1873. Many other keyboard configurations have been proposed. And yet QWERTY persists. So sometimes people keep using something, because it just works or the benefits to something else are not that great. There is not some inevitable need to replace every technology. And mindless embracing change as always better can lead to lots of problems.)