Are you forgetting the weather and how poorly prepared most of the British are for it? Even in new build pedestrianised areas like.. Coal Drops Yard, outdoor seating is limited and normally nearly empty once the midday heat has passed.
I haven't spent a lot of time in that immediate area but I'm not sure why that complex wasn't designed with more of an outdoor orientation. That's not universal in London. I'd say Covent Garden and Camden Town were at least somewhat more outdoor/quasi-outdoor friendly.
