That would be correct if there was also not a plethora of US, German and Soviet content we could also still add for the WW2 era if we wanted to also fully explore them. That argument doesn't just work for Britain.
The point is the community wanted and continue to want more focus on the later areas of the game. WW2 content was the primary focus of the game for 4-5 years.
Whilst we have not stopped adding content from that area, you also should not expect to see a huge amount of diversion of resources to an area the playerbase as a whole dont want the focus of development to be on.