Since they aren't upgradable. The thing is video cards get obsolete quicker than the rest of a system. This looks like it may be starting to change, but so far, they are the component that benefits from the most frequent updates. You want to buy less video card more often for optimal performance. This is true for gaming, 3D visualization, CUDA, whatever.
Well here you've two high end cards, which would imply high end tasks... and no way to replace them when the time comes. That is not a good situation. I mean I suppose you can replace the whole system, but that is rather wasteful. It is also predicated on a new replacement being available and Apple has shown a lack of interest in keeping the Mac Pro line up to date.
To me, this looks more like a shiny toy that people want to show off. "Oh look, I have the most powerful system EVAR! It is amazing!" rather than any consideration of usefulness for a workset, which is what a workstation should be.
Also what the people who are playing the price comparison minuta game miss is that yes, it isn't a bad price provided you need precisely what it is providing, but as the parent pointed out that is rare. The idea with an expensive workstation should be you get the components you need, not the ones you don't. Two GPUs might be great for videogames, they are useless for 3D EM simulation. Conversely 64GB is more than you can use for any game, but is entry level for 3D EM work, you could use 256GB or more for many simulations.
When you are spending multi-thousands on a workstation, it really should be custom to order. The money should go where it is useful to your application set. Trying to have an "everything and the kitchen sink" approach and then saying everyone should meet that is silly.