Language is not static in its forms or meanings or usage. Either in time or in place (dialects). It is a fluid, living, ever changing creature. It creeps, downwards, upwards, and sideways.

'Enormity' has simply shifted in meaning. Interesting that another word of similar meaning, 'wicked' is undergoing a revision of meaning, in this case a reversal from 'bad' to 'good' through its use in an ironic, rebellious way by the youth generation of the 90s. The English language is wicked in its enormity don't you think? Awesome!