Nothing ... its the EOS server which is restricting your participation. I see this as a buffer against liability; the SEC is the US will see that EOS attempted to restrict people from labelling this as a security. Essentially if you live in the US - you have to use a different country's internet to BUY in. It's a buffer against legal action against EOS by the SEC. I don't think its illegal to participate in this ICO either.
RE: EOS ICO begins in only 24 hours, so get prepared