4K HiDPI monitors come in inconvenient sizes if you want two of them
It used to be that I used the same monitors at work and at home, although at home I had one of them instead of the two at work; most recently this was one of Dell's 24" 16:10 1920x1200 monitors. Several years ago I upgraded my home setup to a Dell 27" 16:9 4K HiDPI monitor. Recently the price of good 4K monitors dropped low enough that I got two of them at work; specifically, I got two 27" Dells, more or less like my home monitor that I was already familiar with. The migration over to them at work has turned out a little differently than I expected, because it turns out that there is a substantial size difference in practice between two 24" 16:10 monitors and two 27" monitors. My work 'desk' (a table) has room for them, but it's become obvious that the resit is awkwardly wide if I want to look at the far corners.
If I was doing this over again and had a free choice, I would get two 16:10 4K 24" monitors, or maybe two 25" 16:9 and live with the slightly less vertical space. However, even if I got to redo my upgrade, there's a problem: there are almost no 4K monitors under 27", and those that still exist are unusually expensive. Dell used to have a well regarded 24" 4K 16:9 monitor, but they took it out of production. LG theoretically has one and theoretically will sell it to you if you're in the US (for not too much). That seems to be about it.
(There also don't seem to be many 24" monitors with somewhat smaller resolution, and 2K on a 24" display is already a lower pixel density than 4K on a 27".)
It's not hard to come up with some reasons for why this could be the case. First off, generally big monitors are more attractive to most people, since most people only have one. Now that it's possible to make economical 4K large monitors, most people buying 4K monitors are probably primarily interested in them. The market for 4K 24" is probably somewhat niche. Second, I believe that the higher the real pixel density is, the more expensive it is to produce regardless of the eventual size of display it will go into. This would push 24" 4K panels to a higher cost per square cm than 27" 4K panels, possibly enough to not be compensated for by their smaller absolute size,
(Based on Wikipedia display size figures, a 27" 16:9 panel has a display area of 2010 cm² and a 24" 16:9 is 1588 cm². A 24" 16:10, such as my old 24" monitors, is 1670 cm².)
There are certainly worse problems to have, and I don't regret my two 27" monitors at work. Sooner or later I'll figure out some way to handle the far edges, or maybe I'll completely reorganize how I work with dual monitors (perhaps so there's one main monitor and a side monitor, instead of the current approach where I basically work in the middle where the two meet).