I think the corner cases are likely hard, but the fundamental mathematical representations of the 3D geometry haven't changed. If the licensing cost of Parasolid and ASICs is reasonable, there isn't really a commercial incentive to create something new from scratch. The current market trend is consolidation as Autodesk and Hexagon when on a buying spree and bought up a lot of CAD and CAM software.
OpenCASCADE used to be commercial, but they couldn't find enough customers to keep on and it got open sourced after a failed commercial existence.
I wish more companies, especially university spinoffs, did this when they failed.
It seems so wasteful that poor marketing or leadership or whatever can lock useful innovations up for years while people better able to execute on them reverse engineer the work and/or wait for patents to expire.
The corner cases are hard, but the basics shouldn't be. I'd normally expect several basic ones and a few good professional ones. But that's not what we see...
We have OpenCASCADE, GCAL and Solvespace. The later two are missing quite a few features relative to OpenCASCADE. Then there is Parasolid, ACIS, and whatever they call the kernel in CATIA. There are a few around. But perhaps there aren't that many ideas for innovative features for people who are interested in the area to create something new.