Because MGs are slow cars. Not performance cars.
Porsche is a valid question, so is Ferrari or anything expensive and fast. Both are owned by people who like fast cars. For example, on ABC news here this week, following the 'AutoItalia' event where they showed Ferraris on the news, they showed one giving it a hit on the grass spinning the wheels violently like it was a good thing along with others revving engines. Would they show a Skyline doing that? Only in negative light, to be sure. The reason is society's pressure on this issue is aimed at a perceived lower status male which is a reflection of individuals as part of sexual selection who also seek to put down such males, 'hoons' are seen as just that, relatively cheap cars and young idiots - low status males.