This is due to my lack of knowledge of how to install Python packages if you do not go through pip or other package managers. At the moment, Cadabra runs the following Python script to determine where to install the cadabra module:
print( site.getsitepackages() )
which will produce
or something similar under
/usr/local on most systems. No idea how to do this 'properly' (if such a thing even exists; Python simply ignoring existing package managers is the source of endless trouble...). If you know more about this, I am all ears.