At some point it makes sense to let go of legacy technology. The world is digital, but the 3.5mm jack is an analog port. So a few reasons to let it go are:
1. Moving to digital.
That logic is straight out of the Samsung 'Next Best Thing' where the lady is happy about the Lightning port being digital.)( Needs a DAC adapter to be able to hear it.
2. No internal space needs to be dedicated to what is quite a large port. That space can be used for something else. You can see how large the part is in this MacFixit photo (
https://d3nevzfk7ii3be.cloudfront.net/igi/fdaWRVGrZhxlZoJH.huge).
Can possibly see this....but not for something as pointless as the rumored second speaker. Stereo speakers an inch a part provides little value.
3. It lowers the cost of manufacturing.
An audiojack is likely one of the cheapest components of the device.
4. It lowers the part count.
But not if it's replaced by a more complex part
5. It may permit the iPhone case to be thinner.
6. It might permit more control from inline remotes, considering that it's a digital interface.