The Evolv Shift Air 2 is a cool case, but (as you say) it is on the large side for Mini-ITX cases and therefore likely has much more mass appeal, since the smaller a case is the more difficult (and rewarding for hobbyists/enthusiasts) it will be to spec out components that fit and have adequate cooling.

Just comparing it to some other popular Mini-ITX cases, 23 liters for the Evolv Shift Air 2 is nearly twice the volume of the NZXT H1 (13 liters), and far in excess of the Dan 4 (7 liters) or the Velka 5 (5 liters). Especially the latter two cases are extremely challenging to build in, and at 8.5 liters the "computer-1" is arguably most comparable to that segment despite its GPU length limitations. It's not a put-whatever-you-want-in-it case, and that makes it a niche offering.

I'm not going to argue that there's no TE tax attached here, especially since (unlike similar cases) it doesn't include a PCIe riser or other electronic components, but it's not way out of range for its market segment.