weight and backpacking.
But Yes, If one would be in in one place for long duration's of time, and weight and bulk is not an issue. And you have other easy means of transport, like snowmobiles, horses, lamas, ATVs, or other motor vehicles, then a great synthetic bag is a great choice.
But the decades I spent dealing with the added weight and bulk of a synthetic bag, trudging days on end for many miles. Compared to the difference I experienced when switching to down was night and day. Like YSMACK said, condensation would just roll off the bag.
Yes I still have my -15 synthetic bag and some other synthetic bags, I use in the winter, fall and spring, when I'm car camping. Why not have both, so one can play it based on the situation, when weight or space in an issue...
But if I were to get serious about backpacking again like I was for decades, I'd buy another Western Mountaineering down bag, and just let my son keep the one he borrowed from be. 1lb and a few oz compressed into the size of a football is wonderful...