As has been noted, at many resorts, even those within National Forest lands, it is against policy to skin or boot up slopes. At resorts with steeper terrain at avalanche gradients, there are legal reasons for doing so. All resorts have safe lower gradient slopes, however I doubt any specify where going up slopes is ok because many of the average enthusiasts would not be able to figure much out and end up going where they ought not.
The above noted, there is also the issue of attracting so many enthusiasts into these resort areas that small local communities become overwhelmed, Thus the better strategy going forward for we enthusiasts is to spread out across our mountains, keeping responsible safe distances from others outside our parties, not congregating into groups that then end up in social media photos making the whole community look like inconsiderate fools. That is in fact occurring already in climbing communities that have suddenly shown up in numbers about Moab and Bishop acting like its business as usual, forcing authorities to shut it all down. The same thing (like a total Nationl Forest closure) will happen to us if they see us acting so in our playpens.