While it’s true that some space is saved, that’s just the messaging Apple wants to push. The real reason is to sell AirPods.
Apple also wanted to make non-removable batteries standard to make devices thinner. They did and it was a huge marketing success that had the tiny side effect of planned obsolescence (oopsie).
I’m not saying we can never progress, but what Apple says and what Apple does are often two completely different things. Their engineers will grind incredible hours to meet a silly goal that management gave them of making something 0.2mm thinner. They can keep a headphone jack or a sim slot if they actually wanted to. They don’t want to.