This is because it appears that Apple has managed to sell through their remaining inventory because the iMac Pro has since been pulled from Apple’s website and is no longer available for purchase. You might be able to find a few units from third-party retailers, but we suppose you probably shouldn’t get your hopes up at doing so.
We’re not sure if Apple plans on returning with an Apple Silicon powered version of the iMac Pro, but it seems unlikely since they wouldn’t necessarily need to discontinue the current model and remove it from the website if they were planning on keeping the lineup around. That being said, we suppose there might not necessarily be a need for the iMac Pro anymore.
The iMac Pro hasn’t been updated for a while and the current 27-inch iMac, when configured with the 10-core Intel Core i9 processor, makes it a lot more powerful than the iMac Pro with the 10-core Intel Xeon W processor, so there’s always that if you needed a powerful AIO desktop computer.