That setup was and may still be available from some suppliers- on aftermarket ignitions
FWIW-- I asked this same question of an ignition designer -
It has to do with the grounding path and the rf radiation.
Appoarantly -the best setup is a proper, fully shielded HT cable -Which is pretty well std now .
The return path is well contained
Also -on the circuit you describe - should there be a loose connection - the radiated rf is fierce and will swamp any of the radios we use .