It can't be an effective interaction device and a server-level resource at the same time. Anyone who is enough of an enthusiast to require a dual Xeon workstation is clearly not who MS is targeting with a single product. Leave the multicore server-grade towers to HP, Dell, Lenovo, etc. because there's nothing to innovate there - you just throw hardware, bought at market price, into a box. What is MS supposed to innovate on there if all you care about is specs/$ and ignore the design and use-case?
I love to have just as much power I can. I'd love to have a multi-CPU POWER9 loaded with a couple terabytes of RAM and a couple flash cards attached to a fast bus, but I wouldn't know what to do with it.
Camera raw files haven't been increasing in size faster than Moore's law.
They can get by fine with a laptop. The Mac Pro is overpowered for them.
Moore's law has slowed down btw and is predicted to end in 4-6 years (2020 - 2022) as it would be physically impossible to shrink transistors any further /unless/ there is a change from the current silicon CMOS technology.
In fact, manufacturers are no longer even targeting the doubling of transistors anymore! Instead they are focusing speeding them up.
Photo editing can be hugely resource intensive. Camera RAW files have been getting larger over time, and all but the simplest edits demand an SSD, a fast processor, and at least 32GB of memory. 128GB isn't unusual for commercial work.
You can get by with less, but sooner or later - usually sooner - you run out of RAM and your machine starts thrashing.
Many Photoshop features are hardware-accelerated, so having a good graphics card makes a significant difference to editing speed.
3D animation definitely needs a good graphics card. So does video editing.
Audio doesn't, but it needs as much raw processor power as possible. I know DJs/producers who are running dual 12-core Xeon systems for their mixes, and adding PCI DSP cards on top.
Surface Studio looks very nice, but it fails to tick most of these boxes. The reality is there's a significant market for creative power users willing to pay good money for multicore server-grade towers for their work.
Neither Apple nor MS are paying attention to this market. The Mac Pro is an underpowered curiosity now, and Surface Studio has - sadly - been hobbled by greed and penny pinching.