They went in there because it was untracked and they had absolutely no idea how dangerous it was. All thoughts of fun and very little of consequence. Sad. Permanent closures within resorts and ones in the backcountry are not to be trifled with. There is a reason that they make them permanent. Not many areas have this, but ones that do, give that closed area a wide berth.
There are several areas that are not a permanent closure but have very high danger. Ten Little Indians on Berthoud Pass is a prime example. It looks great, but the near permanent cornice and frequent slides back there make it probably the most dangerous spot on the pass. In the 8 or so years I have been riding there, I have never put a track in that spot. The conditions have always been too sketch when I've been in that area.
Anyone with basic avalanche knowledge would probably (and I stress probably)have not been in that area. I read one person had a beacon, but anyone with or without knowledge can own one of those. I see plenty of examples of this every season.
Enough of my high horse. These people paid the ultimate price. My condolences to their friends and family.