The trees are the most fun parts for lots of skiers. The added obstacles and challenge, as well as an often more beautiful view of nature - I only see interesting birds and squirrels when I'm cruising through the woods, rarely on the groomed trails. It also provides deeper, softer snow that feels like gliding, rather than the groomed trails which are more predictable, but a different texture and a feel that some skiers don't like as much. On a personal note, I have balance and orientation issues that make me dizzy if I don't have trees to orient myself upwards with and I'm guessing I'm not the only one. You're absolutely right though, tree wells are terrifying and not something to take lightly, ever.