I know with at least the Saturn for example, the cheat devices could be used to play imports and/or copied versions of games to defeat the console's AP as a function to enable its cheat features. Depending on the system, there's also additional propietary hardware (memory card/USB dongles) that they depend on to store and update codes with that also has to be verified working.
And, of course, there is the eBay scalper factor.