You are jumping over a key step in the development from blues to rock. There wasn’t just black blues followed by white rock. There was nascent rock that was still a black art form, but a very sexually expressive one (whence the very name of the genre) – the folk art wasn’t just about expressing Black hardships, but also getting down and getting nasty. Once you consider that interim stage where some rebelliousness was already present, it isn’t hard to see a smooth evolution from one genre to another, albeit early white rock intentionally purged the sexual element.