When I bought my truck, I had quite a long list of objectives, all broken down to must haves and various degrees of my own particular wants, but monthly or yearly numbers sold were just not included. Two manufacturers, of which both were looked at and driven, appear to have sold more, but just didn't make my own final choice.
I, like most BMW motorcycle riders, believe that should someone suggest their brand is better because it sells more, probably are not capable of providing a convincing argument.