So I'm assuming they want no one to buy the base config because a base iMac Pro has a better video card and more SSD space for less price.
I think the assumption is that consumers will modify the base model accordingly. I agree with you that the base configuration is not meant to actually sell - sure, they'll probably sell a few to wealthy people wanting "the biggest Mac I can get for a home computer". What they've done is to provide minimum specs for workloads that stress a
different part of the computer.
For example, I imagine that a musician working on highly CPU-intensive, RAM-intensive compositions will upgrade the CPU and RAM, probably beyond where the iMac Pro can go (or close enough that they think they might upgrade beyond that in the future). They'll stick a couple of custom audio interface cards in it, and they're likely to use additional PCIe cards for storage. However, they'll keep the 580X, saying "it gets Logic and ProTools on the screen, and that's pretty well all I need a GPU for".
Conversely, a 3D modeler whose calculations are performed entirely on the GPUs may well order dual Vega II Duos, but keep the 8-core CPU, saying "it's plenty to run the macOS, and that's pretty well all it's doing - anything heavy is getting handed off to the big GPUs, and those are REALLY big".
A Hollywood editor might well upgrade CPU, GPU and RAM and add the playback accelerator, with a relatively balanced workload several steps beyond what any iMac Pro can handle.
There may even be specialized applications where 32 GB of RAM is plenty - if everything is happening in the processor cache (some small, but fast financial models). They would need the high-cache CPUs that aren't in the iMac Pro, possibly the GPUs (depending on how the models were written), and the thermal headroom.
None of these uses a base Mac Pro, but they all use
different upgrades.