The main reason I say that the Crane have some responsibility for the continued existence of the Shadowlands is because how they caused the topic to be treated. The Crane had a great deal of control over how the top tiers of Rokugan treated various subjects. The Shadowlands, the Taint, and everything to do with Jigoku became a taboo subject as a result of their actions.
Granted, they may not have intended this, but they the Crane HAVE controlled the Courts for centuries and they HAVE had a strong disdain and dislike for the Crab almost since their foundation. Things only got worse during the reign of the Fifth Hantei, when the First Yasuki War happened.
Basically, rather than make Fighting the Shadowlands something that everyone in Rokugan should openly honor and do, the Crane made sure (intentionally or not) that the Crab's war against the Shadowlands is seen as an unfit topic for polite conversation, and almost no one goes and helps them. Granted, there are many other factors at work here, the horror of fighting the forces of Jigoku, the need for their to be more to life THAN fighting Jikogu, and on and on, but the fact remains that the Crane treatment of the Crab is... distinctly dishonorable from an objective stand point, and is never seen as such by anyone.
That's all my personal take on things though. I can't deny that the Crane DO produce great heroes (and villains), or that they can make breathtaking art. It's just that nine times out of ten all of that serves only the greater aggrandizement of the Crane. That's a problem with most Clans, but the Crane ... eh they just rub a lot of the fandom the wrong way, probably because of differences in cultural values.