Well, if you are sitting at a desk, you can only go so big before it starts to get too big. I was a 24" monitor guy for a long time. Went to 27" about 3 or 4 years ago. Now at 4K I'm starting to want 32" (I'm getting old, text at 4K on a 27" is starting to get squinty for me), but 42" is just waaay to big for me to use and sit comfortably. I have a 42" TV in my den by the fireplace. I can't imagine that sitting on my desk. I'd have to move my desk out from the wall a good foot and mount that size monitor to my wall to feel comfortable.
Now, I know a lot of you guys are using 42" (and larger) single displays. To each their own. I really wanted a LG OLED for a monitor, but just couldn't get over the size, even at 42". Now some smaller sizes are finally starting to pop up.
I do miss 16:10 a lot though... 16:9 just feels too short for the width, or too skinny if you try to rotate it.