As I understand it, primarly because due to the high energy level of x-rays, light x-ray interacts very differently with materials[1]. Primarily they get absorbed, so very difficult to make mirrors or lenses, which are crucial for litography to redirect and focus the light on a specific miniscule point on the wafer.
The primary method is to rely grazing angle reflection, but that per definition only allows you a tiny deflection at a time, nothing like a parabolic mirror or whatnot.
All of these problems or equivalent still exist in EUV. Litho industry had to kind of rethink the source and scanner because it went from all lenses to all mirrors in EUV. This is also why low NA and high NA EUV scanners were different phases.
As I hear it, the decision had large economic component related to Masks and even OPC.
100%. EUV barely works. XRay litho takes all the issues with EUV and cranks them up to 11. It will take comparable effort to EUV, if not more, to get XRay litho up and running, and I'm not aware of anyone approaching this to anywhere near the level of investment that ASML (and others) have pumped into developing EUV tech. We may get there eventually as a species, but we're a ways off.