I just like 200+ PPI displays (24" 4K is the same pixel density as 27" 5K) because I have to spend a lot of time reading text and like not seeing pixels and/or anti-aliasing artifacts. Once you get used to it, going back is like going back from an iPhone 4 to some Windows Mobile 6.1 phone.
It should also be cheap enough now, and at some point fabbing a 200+ PPI display will cost the same as an older one, it won't make much sense to keep making the lower res displays anymore (like it doesn't make sense to fab 32MB DIMMs anymore).
Don't get me wrong, I agree when the tech gets better, with none or few of the downsides others mentioned, going forward is the only direction. I won't actively shop for an older tech once the current one gives up the ghost.
I just disagree that it's "time to upgrade your monitor", or that the current tech is bad or makes it hard to be productive.
It should also be cheap enough now, and at some point fabbing a 200+ PPI display will cost the same as an older one, it won't make much sense to keep making the lower res displays anymore (like it doesn't make sense to fab 32MB DIMMs anymore).