They maintain all these architectures in such a small, consolidated codebase with such minimal (if any) bloat.
Their built-in httpd is far and away the best experience I ever had setting up a static file server for my local network, and I can't think of many times where I would ever need anything I couldn't do with the built-in FastCGI support.
I'm also pleasantly surprised by how well Chicago95 (a Windows 95-style UI based on xfce) works on OpenBSD, even though the author never intended to run it on anything but xubuntu. I wouldn't recommend trying that unless you're willing to roll up your sleeves, but the payoff definitely justifies the elbow grease if you like that look and feel better than xenodm, XFCE, or GNOME.