The main reason Nintendo would buy EA is because they can (1) restructure the company to make it NOT bleed money, (2) obtain all of their IPs, (3) obtain all of their talented developers and put them to good/better use.
Point #2 is the biggest.
Buying out a company that's facing financial issues has for decades (centuries?) been a major business strategy. If there's a possibility that the company can make money via a little restructuring, or that company owns something very valuable to your own, then it's VERY common to buy out the "flailing", "dying" company.
It's like buying the Titanic after it's hit the iceberg... because the ship's hull is made of gold encrusted with diamonds. YEAH it failed, that's fine, but it's still potentially worth a crapton.
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