You're right that it's to do with the size of the market - 300 million potential customers is a huge amount of growing room. However, the UK has 60 million peo

You're right that it's to do with the size of the market - 300 million potential customers is a huge amount of growing room. However, the UK has 60 million people, not 20 million (I thought you were talking about the adult population, but you referred to the total population of the US). Also, the difference between US and British English is so slight as to be irrelevant. I think the lack of a large domestic market is one cause, however I'm going to say the main reason is that we don't have a Valley in the UK.