In reply to TheFasting:
IMO it's because it is fickle or as Simon Richardson recently put it "Ephemeral".
When it's truly in, it's fantastic and reasonably accessible (as Patrick R said- life affirming and without travelling the globe!)
When it's not in, it's frustrating and depressing- many throw the towel in.
It's the true rush to get something done whilst it's in. You cannot say "I'll do it next week". It's in tomorrow am and might be gone by evening! It's the satisfaction to have done the maths to be at the right time at the right place, in the right frame of mind with the right person.
It offers such a breath of fresh air to week-end warriors like me.
It offers a unique possibility to stretch oneself, and without being particularly talented being recognised by peers (the scene is not that big in my view).
It rewards doggedness.
Obviously, for those operating at the higher end of things, talent and dedication do play a huge amount. They (old generation and new generation in their own way...) are very inspiring and approachable. You are likely to meet them and/or see them do their stuff. You'll want to emulate this at your own level.
it's just a great way to spend time with your mates.
All of the aforementioned factors make it a perfect recipe for a culture of winter climbing.