They would do. A lot of those maps are specifically made for taking screenshots, taken at highest alpha multisampling (not in all cases though) settings, or scaled down from ultra high resolutions. It's mostly to see what the engine is still capable of doing, albeit not exactly at playable rates... it's just showing it can render all those vistas and effects together, but there's a reason nobody's retail Crysis actually resembles those screenshots.
The maps in the screenshots aren't even remotely playable - you'd turn around and all you'd see is an empty void because that's all that consists of in most of them. It's like a hobbyist kinda thing in the Crysis community.