The headphone jack isn't just a hole though, it has electronics that take up space in the internals which manufacturers want to use now for other things.
- Other manufacturer are managing to still cram an audio jack into their competing smartphones
- Smartphone are getting *wider* with *larger screen* each generation. In theory they should have *more room* for electronics.
- The "other things" might not be as useful as marketing would like you to think (Apple's taptic engine was the excuse for removing their jack).
- The only reason that manufacturer are lacking space is because they have launched themself in a competition for the thinest device possible. By trying to shave a few mm of thickness, they are losing critical space. This has already cost Apple their bendgate (less thickness = less mechanical resistance) and caused Samsung a few exploding batteries (not enough space for battery expansion).
In other words: I manufacturer weren't competing for the first company to release a phone thin enough so you can cut cheese with it, they would have plenty of space to keep a phone jack, add their useless new features AND have bigger batteries with better life.
I get why people want to hold onto this legacy port, it's a well established piece of tech that has been tired and true and remained unchanged for decades but to say that there's a pen hole so a headphone hole is the same thing isn't really accurate
The total volume of a pen, is still bigger than the volume of small compact jack connector and the tiny DAC feeding it.
No the real excuse is getting a way to sell either extra dongles (audio-out to USB-Otg or Apple Lightning)
or expensive accessories (force you to buy Bluetooth Wireless earphones. Or wired phones with custom plugs).