Because current X implementation is completely screwed up. Instead of rendering on server and sending only high-level messages like "here be buttons", X's rend

Because current X implementation is completely screwed up. Instead of rendering on server and sending only high-level messages like "here be buttons", X's rendering everything on client — even rasterizing fonts, then sending bitmaps over network. Obviously, volumes are huge so is latency. And there isn't even a slight hope of look-and-feel consistency, too (how client on remote machine is supposed to know your GTK theme?) Wayland may seem weird, but it could be a step in a right direction. Just throw in network transparency at widget toolkit level.