The generate_pyi.py script needs to import the modules that it is generating .pyi files for. For static builds, this means that it must import the special "static importer" module.
Note that VTK's own "static importer" module is already loaded by vtkmodules/__init__.py, but similar mechanisms are not always present (or even desired) for other wrapped packages, e.g. Paraview's.
Backport: paraview/release