That's really a forecaster discretion kind of thing. I'm not aware of any policy that states all offices should use "showers" out there, but I know around here we generally try and focus on what will public perception be.
Like if we're going to upslope and I have likely PoP, and there are always flakes in the air, the public is going to say it's snowing, not there are snow showers. So I'll change all wx at 55% PoP or greater to stratiform.
It's possible the terrain out there is so unwieldly with the grids, that they do showers for ease.