I just think Western gamers prefer different, more mature things. Again, correct me if I am totally wrong.
You're totally wrong
At least in assuming the majority of western gamers prefer... "more mature things"... I don't even know what that means. Blood? Violence? Nudity? Or simply "not kiddy/cartoonish" things? Or is it storytelling? There are plenty of great examples of very mature and wellmade storytelling in Japanese games... and even with Nintendo games. Ever played Fire Emblem: Path of Radiance and Fire Emblem: Radiant Dawn? Two of my favourite games of all time due to the story that spans both games. Tackles a lot of really hard issues such as racism, genocide, religious zealots, etc, etc.
There are some games that do fall into the extreme areas where "only Japanese people would like this" or "only western people would like this" but those are pretty niche kind of games for the most part.
Though, one truth to acknowledge is that western games tend not to be quite so popular in Japan. But Japanese games in the west? Extremely popular with many people for many different reasons, not just because it's a family game or a really weird animu thing or whatever.