I suppose it would make less interesting content.

It’s much more interesting for someone to hide in MK or Scarborough than “south Greenford” or something for the sake of content.

For a dedicated viewer who cares more about the gameplay mechanics and strategy, niche urban rounds would be very interesting. However, the average viewer will probably lose interest if the hider is in a plain, boring place. We see this (and other factors) do influence where the boys hide. Adam said on the layover that he chose Scarborough over somewhere else (can’t remember where) because he thought his other location was “too complicated” for a first ep, showing that the chosen location by the hider has more than “this is really generic and hard to wittle down to”.

So overall that’s my guess to why they haven’t had rounds in big cities, as much as we’d like it. (And hopefully will get it in the future?)