Nuggetau is right.
They simply do not have enough power. And I rode the Berg 650 with a turbo even. Also a KX450, as well as a 570. Both powder and spring snow.
I felt as though they ride through the snow, instead of ever getting "on" it.
Dirt bikes are my life, and yet I couldn't wait to get my sled back after having traded for an hour. I really WANTED to like it. Riding on the "trails" to get to the high country was a nightmare as well.
Perhaps with 100hp or more it would be different?
Additionally, I feel like its very hard on the motor. Never would I (or need to) hold my Bergs WFO when riding, like is sometimes needed when on the snow. Perhaps motocrosser's do, but I have yet to hit the rev limiter on my new 501.
Just my thoughts to help the original poster. I do not mean to offend anyone, nor wish to start a debate.
Regards