Had no idea WM is so popular and brit so unplayed.
The main reason why brits are the least played is because they are the newest faction (and locked behind a DLC). Wehr is pretty popular because it's part of the base CoH2 package and I guess more people think it's more interesting to play as the axis as they probably are more "WW2 iconic" than the allies factions. I see a lot players in automatch who use the names of Wehrmacht Generals or important Wehr divisions as their steam nickname.... and most of the times they mainly play axis only. But I barely ever see people doing that with Generals or armies of the allies.