The iMac Pro was one of the fastest machines Apple had made, however, production for this one device has been permanently stopped, leaving only the $4,300 version. These devices are only in stock but when they are gone, they'll be gone forever.
Now the only "Pro" model by Apple is now just the Macbook Pro, powered by the M1 chip. The iMac Pro product is still alive on Apple's website, but the stock is now very limited. Retail partners such as Best Buy and Amazon have listed the product as unavailable for delivery and pick up. Apple is planning to make new ones soon this year, however, they refused to make any big changes to the device. There may be a small chance that the device is still available in your area, but don't get your hopes up, these devices are known to have unbeatable performance and people may try to get one for the very last time.
Rumours have been spreading around for a while now that Apple will make a whole new iMac, powered with the M1 Chip, and thin bezels, a colourful exterior, and more!
This reason to discontinue the iMac Pro is maybe that Apple simply sees no value in it anymore.
We can't predict how this will go, but we can only wait until the company rises to say something.