Maybe because Three Mile is actually American? Perhaps Windscale garnered less coverage because it happened in Britain.

I am not writing from an American perspective, this is true in European media as well. In any case, you’d think that an accident releasing radionuclides all over Europe would be a better example of the dangers of nuclear than a security system shutting down a reactor as expected in case of emergency. It’s all academic anyway, these discussions are not exactly rational.