Because creating unique intellectual properties and developing them requires time, resources and adequate financing. By producing commercially successful titles - regardless of them being action RPGs or not, but action RPGs was the provided example - they can generate enough revenue with which to finance risky endeavours such as going with an in house IP which is less mainstream. "More profound" RPGs aren't as commercially successful as more mainstream RPGs, and trying to develop them without any considerable monetary backup can be damning. Trying to establish reasonable funding from titles which may be commercial success is better than trying to establish reasonable funding from titles which may be commercial failures.
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Indeedy. Just like the music industry is discovering: just because the media companies are multi-national, doesn't mean they can leverage their econmies of scale to market a particular band / genre / trend / whatever.
In fact the trend seems to be more smaller market niches. Which the music industry is financing with imbecilic teenagers' pre-occupation with being "different" exactly like the rest of their peers, buy buying the same type of rehashed pop covers that get released in a cycle a couple of years apart.