It's probably because AGPL is a bit too restrictive for traditional server software. even if you don't provide your HTTP server(e.g. Lighttpd) code to users who visit your static HTML website, it doesn't harm user's freedom. But if the code of your HTTP server is AGPLed, you have to provide the code of your server to users who use it even when it doesn't help improve user's freedom fundamentally. (1/2)