If you have 20/20 vision, a 27" display at 1440p (~110 DPI) has a visual acuity distance of 79cm - ie, if you are sat 79cm or further away from the screen, humans are not capable of resolving any extra detail from a higher resolution. High refresh rate 1440p IPS screens are very widely available at good prices, so it isn't that crazy that people choose them.

Phone and laptop have higher DPI screens of course, but I'm not close enough to my desktop monitor for a higher DPI to matter.

That's a common misconception. That acuity calculation is based on knowing nothing about the image; imagine applying it to arbitrary noise. When you have things like lines and edges your eyes can pick out differences an order of magnitude finer.

https://en.wikipedia.org/wiki/Hyperacuity

I'm running a 32" display at 4k, which works out to about the same at 79cm. Apparently a bunch of people sit really close to their monitors :)

Have you tested it in practice? High-DPI monitors make a very noticeable difference for text and user interface. That's the truth, even if the theory doesn't agree.