People tend to lump in the Sega CD with the failed systems, but it was actually the most successful console add on ever, supporting over 200 games.
This was part of the problem with the 32X. Sega USA ran with the CD and turned it into a success when Sega Japan didn’t want it. When Japan was prepping for Saturn, US demanded the 32X and when Japan said “no”, US said “yeah, well, look at Sega CD, what do you know?” Sega USA arrogance willed the 32X into existance and, well, you know the rest.
Guitar Hero sold more, but how many games USE the guitar? 4? 5?