There are so many other places that the US has no reach. Why would someone in Iran use a US website to buy bitcoins?
Why even post here, it's not shocking, Coinbase is doing nothing wrong. I know the US want's too much control over the world, but it's not the people's fault, it's not the companies fault. Don't blame the people or the small companies.
I suppose its because there are not a lot of secure options in other countries to use as a web wallet . Also I haven't ever used the wallet, but I assume it does not clearly state that other country residents are not allowed to use it(but I might be wrong with this) .