Where they had good distribution they were top sellers. In the UK when KN6000 ran it had 50-60% market share at its price level of the whole market, not just against PSR9000 alone for instance. 6500 and 7000 also did very well there, Germany another good market. Where the distribution was useless they did poorly, US distribution was always poor. UK trade figures show keyboards are a declining market year on year.
At the end of the day Music Instrument Division was a tiny part of Panasonic/Matsushita, and probably had a fraction of a percent of the turnover of the battery division for example. Japan has been in stagnation for over a decade and the accountants have spoken. Thus is our Brave New World.