But that space usually isn’t. No company would make a battery with a tiny little protrusion where the headphone jack once was. That’d cost a lot more, and make it a lot more fragile.
They’d be more likely to leave it empty, or fit something else in that space, like a third speaker.
It would also let them claim that its an open standard that anyone can use and they’re contributing to open source, even if no-one could effectively use it in the same way that they implemented it.