Because its much slower than sending directly to customers, more expensive than sending directly to customers, increases stock holding (unless you want premining) and generally doesn't help.
Exactly, I don't see why people think that the UK seller won't have to pay all those fees to get the stock into the country in the first place, and then pass them on to the customer with an additional markup.
You can not see the argument because you / your arguments are narrow-minded.
If bitmain decided to hold stock in the UK (even EU), they'd DEFINITELY get a better per unit shipping rate (when they ship in bulk to the EU) which can constitute their mark-up to cover their overheads; I argue that it would be enough to even book a real profit NOTWITHSTANDING that the actual price to the customer will not be increased.
It is up to bitmain to identify their best "locality" in Europe (UK, Germany, France etc) such that postage in that "locality" will be even lower than the other outer reaches of the EC. They'd be a tax collecting point and effectively reduce the time it takes their customers to get their orders.
To argue that it takes longer to ship within the EU than it is from China to the EU is, in the light of day, as counter-intuitive as it is ignorant. All it takes is planning ahead.
By the way, the same argument could hold true for the Americas, but I will not argue their case for them.