With higher resolution monitors and higher pixel density, web pages and images start to look smaller. If you have a 4k or 5k monitor, you might as well be looking at a postage stamp. However some apps and browser try to scale up and results are less than optimal. You can now enlarge your viewing experience on this site by selecting a larger screen width from the Settings menu on the top bar. This will make things a lot more pleasant to look at.
Remember to reset your browser to 100% view if you go with the larger screen width options.
Yes, I see what you mean. I have a 4K monitor that has 7 MP display. I guess we will have to start posting bigger pictures. DO you have a limit on size?