// why do advertisers choose to have mainly black and white models and even black and white cartoon characters showing off their products, so as to represent the people of a majority white country? //
The Womens World Cup image is not aimed at a British audience, it is aimed at a worldwide one. Whether viewed in Africa, China or Europe, the figures are recognisable as women. They do not represent only black women, that is just your graphical illitracy kicking in.
Your general question about advertising models is based on your exposure to it. The advertising you see is aimed at a UK audience not a worldwide one. Adverts in China feature models from that region, in Africa, they feature African actors. The UK is mostly white but not exclusively. So while the majority of advertising features mainly white models, there are plenty of black models also. Which corresponds with our diverse society here in the UK.