Because most people pick monitors by size, not resolution and PPI.
4K is also popular because it fit within the capabilities of common HDMI and DisplayPort ports on people’s computers and cables.
If you try to sell a monitor that doesn’t work well out of the box with the average laptop, it’s going to have an extremely high return rate. That’s why display resolution will always lag behind the common capabilities of your average HDMI port on a cheap laptop.
4K is also popular because it fit within the capabilities of common HDMI and DisplayPort ports on people’s computers and cables.
If you try to sell a monitor that doesn’t work well out of the box with the average laptop, it’s going to have an extremely high return rate. That’s why display resolution will always lag behind the common capabilities of your average HDMI port on a cheap laptop.