The detail you are missing is that one has to buy an additional enclosure and the set of PCI cards is actually limited, hardly workstation class.
This is a workstation,
https://www.dell.com/en-us/shop/desktop-computers/precision-...
Interesting that all the memory options are "no longer available".
Damn, that Dell case, fancy Xeon processor and nVidia card must really be worth a lot, because the rest of what you get for $9k is 32 GB RAM, a 512 GB SSD, and a Windows 11 Pro license, all while consuming hundreds of watts of power.