Presumably the vast majority of people are not going to want to scale their 13-inch display so that everything is significantly harder to read for the sake of increased screen real estate. But I'm glad that the MacBook works well for your specific use case.
I currently work on a MacBook Pro 13 and I switched from a XPS 13 with a 4k display. They're largely comparable, and the only difference I notice or care about is the OS. It seems that is how it is for most people.
When I use other screens (including the iPhone SE I'm typing this on) the reason I struggle isn't lack of real estate, it's everything looking so massive and oddly hard to read because it's too big.
It's not just the pixel density, it's not allowing me to scale everything way down. The smallest font in settings is too big. UI elements are too big. With the keyboard open writing this there's about an inch high of the actual page visible, barely more than this textarea itself.
(It's the old SE, FWIW. Bought a refurb to try iOS when my Android phone broke. But the repair for that was arranged right around when lockdown started so I've been using this for longer than anticipated. Not the polished 'just works' experience I expected, the a priori known restrictions on changing default apps, browsers, etc. aside.)
From what I noticed Apple seems to relatively okay at this. On Android the typical app redesign has the key feature "we made the previews larger", which is always an infinitely stupid idea, because the main view of most apps is a list, meaning you want some overview over what's available. Soundcloud and Spotify (there are many more I can't think of right now) seem to think that a gigantic either very obstructed or totally generic cover is better than being able to see multiple titles at once (what the fuck - doubly so since Soundcloud removed the most awesome feature of showing a wave form preview - newer versions coincidentally only show you a portion of the wave form in full screen in playback mode).
Setting a custom DPI only helps a little - side elements like nav bars do get smaller, but all the layout is still completely the same, like everything is designed for a tiny phone (which absurdly nobody makes anymore).
What are designers thinking? Is it really just short-sighted "look, we like content" and "but pretty", or is it something that actually improves UX for most people and just leaves me bewildered?
I currently work on a MacBook Pro 13 and I switched from a XPS 13 with a 4k display. They're largely comparable, and the only difference I notice or care about is the OS. It seems that is how it is for most people.