It's by design because the vast majority of people don't care about that information and it makes the website worse for them to have a big ToS banner at the top of your page.

I don't think many websites have a secret ToS that they hope you won't read, I think most of them don't even know what their own ToS say. I signed my lease on a site with an explicit checkmark for ToS that said I agreed I would only use exactly IE7 to use their site.

Which is plenty amusing, until one of those companies is suing you in a court of law for violating said ToS.