I don’t get why you get so much downvotes, because it’s not as obvious as people make it out to be and there are plenty of adapters. So it’s a good question.

But yes. The 3.5mm jack had the thing companies say they are striving for: simplicity.

DACs are nice and everything but the phone can just decide to not connect properly. The DAC can decide it had enough of your phone. In either case you’d need to reconnect them. And that means unlocking your phone, because a secure phone will block streaming to ‘unknown’ USB-C devices, unless it’s unlocked during the negotiation phase. And if your connectors have become wonky for whatever reason: Well, no music for you.

And then there’s the issue where you have to have them at hand when you need them. In your car, on your person, while at work.

3.5mm is great because it actually “just works”. One of the few things that can claim such thing.