My answer, as someone who rides the fat in gnarly and tame terrain, downhill and uphill, and having won DH fat mtb races:
Fat bikes ride inherently different in the snow. They are rigid, but they do not ride like rigid fatbikes do in the summer. Some of the differences are the self-steer phenomenon, which is gone in snow, the tires obviously absorb a lot of terrain at the right PSI, the snow compresses and further absorbs impact, snow fills in between roots and rocks, making the impacts smoother, and you generally don't reach the same summer speeds, because you aren't limited so much by your suspension or lack there-of, but the grip of the tire against the snow in turns. If you try to go too fast, you wash out, this is where studs help IME, for not-just-icy conditions, as I can edge more. Still, if you go too fast you'll get suspended-with-no-damping bouncy, but it's more rare. It's fun to do doubles and tabletops in the snow in the fatbike.
It's for these reasons that I don't ride the fatbike in the summer, it bounces like crazy, you have more grip and therefore more speed, you get significant self-steer where the tire tries to continue turning into the turn, huge amount of gyroscopic rigidity that causes the bike to ride up the berm and towards the outside of the turn when trying to turn at speed, etc. Also, the suspension fork would add about 3.5lbs to my front end, making it harder to loft, etc. A few people run them, they aren't super common up here. I think people probably buy them more because they are coming OEM on some bikes.
If you're going to ride it in non-winter conditions, get a suspension fork.
