In many cases those error messages are used when something there is nothing the user can do about it. So there's not really any useful info to provide. It's not uncommon for websites to have integrations with other systems. For example, if there is a backend system involved that returns an unexpected error code when the website makes an API call to it. Or if the backend system is unavailable (network outage, down for maintenance, etc). Often (but not always) these are caused by rushed or sloppy code.