There are four factors that can affect glide regularly in fresh snow.
1. The wrong flex.
Powder snow is more sensitive to an overly stiff tip than transformed or corn snow. I doubt that this is it, but the one model of skis that really comes to mind here are the red and white/silver Xium skating skis.
2. Too aggressive structure on the base.
Powder snow, especially here in the mountain west due to our arid climate (even when it is snowing, or especially even) is very sensitive to too much structure. A "universal" structure around here except for the rare exception is a fine or cold grind.
3. Base hair.
If you have "hair" on your ski bases, this will slow the skis down especially in powder snow. Corn snow is not so sensitive to this. My experience is that skis can become this way by either a poor stonegrind or using a steel brush. You can see and feel this hair if you know what to look for.
4. The bases simply don't have any wax in them.
This happens with new skis quite a lot. Again, powder snow is far more sensitive to this then corn snow. This year I got a bunch of new skis and then I got injured so I wasn't able to ski them in. The skis aren't holding the wax at all. They look matte and become white or abraided after just a bit of skiing.
The solution is to do applications of ironing in a soft wax (yellow), scrape and brush, then a hard wax (blue), scrape and brush. Do this cycle whenever you wax your skis. It will help. Also, be sure to use enough heat to get wax INTO the base. The base needs to get pretty hot. Many people just make the wax liquid which with yellow happens very easily, but that won't do you any good unless the base is heated to the point where it expands and allows the wax in.