A game designer needs to consider two factors when deciding a battle system - how much it will rely on quick decision making / reflexes, and how complex to make it. A more real-time combat system will cause adding complexity to the combat to increase the learning curve and difficulty more because making decisions in a more hectic/time-constrained setting makes most players either make worse decisions or take the same amount of time and let the time restrictions take their toll, so that most developers who don't want to alienate all but the most talented players tend to choose a spot on a spectrum with one side being turn-based and complex and the other being completely real-time with almost no strategy.

An example of a game that tried to add too much complexity to real-time combat is The World Ends With You. Of course it was great and well-reviewed, but the devotion required to do well in its combat system probably turned off many potential buyers, hence the good but not phenomenal sales.

With that said, I prefer turn-based combat. If I wanted to test how fast I can make decisions I would not be playing a genre with its roots in complex decision-making.

TWEWY didn't sell better because of it's Japanese motif which limited it's audience, not because of the complexity of the battle system.