They are fulfilling the orders. The fact that it's taking longer than people may want doesn't mean they aren't honoring the orders, and nothing about pre-ordering would have been taken to guarantee or even to suggest a time-frame.
If you go into a restaurant and you're the only one there you can expect your meal faster than if you go in at the busiest time - and if you go into a McDonald's at the busiest time you are going to expect your meal a lot faster than if you go into a Michelin Star place at the busiest time. A camera lens, even a low quality one, is not a mass-produced item. There is a hand-made, artisanal characteristic to this sort of thing - especially a higher quality one like we all expect from Nikon. There's only so much they can increase production even if they put every last resource into making one product alone - and I don't think it's reasonable to expect a company to do something like that.
Think of it this way: say that they opened pre-orders on a lens and then literally every person on the planet ordered one. I'd think you would understand in that situation if they couldn't meet the demand very quickly. That's an extreme example, but the point is that at some threshold demand is going to outpace any ability to try to meet that demand. Remember when hand sanitizer was impossible to get for months and months in spite of multiple major international companies shifting most of their resources to producing the stuff? I can understand being disappointed and frustrated at waiting to get an item like this - I am waiting, too - but I don't think it is reasonable to think that the only possible explanation is negligence or bad faith.
@SCoombs - The restaurant is a bad analogy because we would all walk out. As @Patty15 says we are tethered to the Nikon system - compelled to eat at that one restaurant using your analogy. We expect our server or even the restaurant owner to explain why food is not prepared (our supplier of potatoes is late in delivery) and provide a realistic statement as to when it will be served (we expect potatoes to arrive in 30 minutes and then it will take 35 minutes for preparation). Let me draft a statement for Nikon with hypothetical numbers and dates:
To our wonderful Nikon customers who have pre-ordered the Z 180-600mm lens. Thank you for your commitment to the Nikon Z product line. We truly value you as customers and are working to fulfill the many orders that have been received without compromising the quality of promised lens. Nikon has difficulty knowing the exact numbers of lenses that are desired because many customers have placed orders at multiple outlets intending to cancel orders once fulfilled by the first outlet. This is problematic for Nikon and we try to estimate the impact of this inflated demand but it is not an exact number. Nikon is currently producing between 1500 and 3000 lenses per month. With the number of orders Nikon has received we expect to be able to fulfill all orders by no later than December 31st. Dealers are allocated lens delivery on a pro rata basis depending on time of order and numbers ordered. Of course delivery by your dealer may depend on where you are in line with that dealer. We will continue to produce quality product and reasonable prices and are doing our best to reward you for your loyalty.
I have no idea as to the numbers of timing but there is great benefit to honesty and transparency.