Obviously there's a strong element of personal preference there. Where I live, winter is cold (temperatures below -20F were common at the ski hill this past winter, even before taking wind into account), and long (there's still some snow today in my back yard). When I take a warm-weather vacation in winter, I want it to be hot, not just "pleasantly warm on the nice days".
So for me, a west-coast cruise in winter wouldn't appeal. But of course lots of people prefer more moderate temperatures, or maybe if you live in a warmer weather climate, the temperature isn't such a big priority for your vacation. To each his own.