I think it's the former; you can't host any site that is supposed to be accessed by the general public, only something like a control panel for your NAS or secu

I think it's the former; you can't host any site that is supposed to be accessed by the general public, only something like a control panel for your NAS or security system or such. This serves to protect them technically (residential systems are not designed to withstand a large number of inbound requests), legally (you can't sue them for failing to serve your site) and of course to promote their more expensive business lines.