Because around here, the socks just don't stop. (And judging by how little progress I've made on them, they might never stop.)
It's funny, though - I can take almost a full week just to knit a few paltry inches of cables, and then in one day I can knit the heel flap and turn the heel. Then when I'm on the stockinette foot portion, it's just a straight shot to the end. I suppose cables just really do require that much more mental energy, and once I'm on stockinette I can start knitting while doing other things.