My last 1080p monitor was around 20 years ago. I have trouble comprehending people still use them regularly.
People also use usable mice instead of touchpads, and they put the "ctrl" key where Apple thinks a useless "fn" should be. All kinds of things happen outside Apple world.
To me, it's more about what I'm used to. I have a perfectly fine several years-old monitor, so why should I throw it away?
The problem is, as soon as you are not on a Mac but Linux or Windows, you are in for an awful, truly awful lot of pain. HiDPI support is a mess because even in the rare case applications are made with HiDPI in mind they are not tested on HiDPI machines.
Other way around, most Mac software is not tested how it behaves on inferior external monitors.
A very quick search yielded Dell selling 1080p laptops today:
https://www.dell.com/en-us/shop/dell-laptops/dell-15-laptop/...
It is very, very common. Just not in the Mac world.