This drift of meaning, technically called catachresis, is as widespread as it is curious. Egregious once meant eminent or admirable. In the sixteenth century, for no reason we know of, it began to take on the opposite sense of badness and unworthiness (it is in this sense that Shakespeare employs it in Cymbeline) and has retained that sense since. Now, however, it seems that people are increasingly using it in the sense not of bad or shocking, but of simply being pointless and unconstructive.
Egregious is a word that has fascinated me for this very reason.
