Sue them for what? When you buy a fleet of cars for your business and there's a recall that takes it out of service. The manufacturer has an obligation to fix the product, they're not liable for loss of use, unless specifically stated in the purchase contract. That insurance is typically an additional option either offered by the manufacturer or 3rd party.

I guess you can try and see if there's negligence or willfully misrepresenting a known faulty product. Or is 400 days turnaround reasonable.

Obviously NK management and their lawyers thought whatever it is they're got from this is fair or it's all they're likely to get considering the risk/reward of litigation.