In the hopes that you are not a conspiracy theorist you must assume marketers haven't done any research about what girls innately like and are purely marketing products based on what you might call 'traditional' views.
It's much easier to market sugar than it is to market broccoli so that's what most foods marketed today contain. I don't believe we like sugarry treats because of marketing. I believe marketers market flavours of sugar because sugar is what we're wired to like first and foremost.