I am speculating here, but I think the US was among the first to realise that access to state-of-the-art computing is a national security issue. Therefore, the US government essentially subsidized IT R&D (e.g. Silicon valley, this is confirmed by Wikipedia) giving the US a huge heads up to the fragmented EU granting/capital (and likely Asian, but I don't know) landscape. Therefore, we now live in a legacy where, although tech is a global phenomenon, it is largely controlled by US capital, with other players (EU, CN, JP) playing catch-up.