Money. Old companies are merged, acquired, or spun-off all the time.
It's completely possible that Nintendo would prefer to spin off portions of their business which, while profitable, no longer align with their primary markets. Consider companies like General Electric; they started off producing equipment around electric power generation, installation, and use (lightbulbs and appliances), then they got into television, radio, computing, jet engines, health insurance, etc. Over the years they've spun off many of these divisions and today's GE looks nothing like OG GE.