I tend to agree but more because the market has settled on it. One thing about screen size is that it's easier to achieve an effective screen size with a smalle

I tend to agree but more because the market has settled on it. One thing about screen size is that it's easier to achieve an effective screen size with a smaller screen (by moving it slightly forward) than it is to do the reverse. So a 24" screen will work in more environments, e.g., smaller desks, than a 27" will. A dual screen setup with two 24's will require less neck movement. Of course, the market has also decided that decent aspect ratios aren't worth doing either. If there were 3:2, 4:3, or 5:4 options—more versatile for productivity—we'd probably settle on something between 21" and 24".