Adults read trashy romance novels. I'm pretty sure Mass Effect is aimed at adults and teenagers. Also, what other WRPGs like it? You've got Mass Effect and Dragon Age. Maybe the first Witcher. That's it. It's like using Hyperdimension Neptunia as a standard JRPG.
TBH, I don't think the issue is targeting children; Pokemon does just fine targeting children. The issue is targeting a niche adult audience that already buys JRPGs without expanding said audience. Children aren't buying Xenoblade, JRPG fans are buying Xenoblade. Only a few series like Dark Souls and Persona have really burst out of that "JRPGs made for JRPG fans" bubble.
Good points. Rather than descending into the cesspit of discussing moe etc, its worth looking at why some JRPGs retain broad western appeal and some don't. The same goes for other genres too.
Final Fantasy changes things up with each new world, so I wonder if some of its appeal is about curiosity. If a westerner (or anybody else for that matter) didn't like the last one, you might like the next. Whole threads are full of people dividing the franchise into the ones they did and didn't like, and that diversity perhaps gives it stability and stops it falling too fast. In contrast, other JRPGs have pissed in their own singular pool somewhat (hai Star Ocean) as they continue to appeal to a niche where more people leave each time, rather than using each game as an opportunity to grab new players.
Dark/Demon's Souls hit the whole online community thing. It's tough, and most forums have a board with people swapping tips- that gave it great word of mouth that has translated into expectations of a real, meaty challenge- it's not everyone's cup of tea but its made a selling point of not forgiving gamers raised on easy modern action games that just need you to press A for awesome. It's not mainstream appeal, but that reputation is great for luring people into the series- anyone getting into gaming will eventually hear its name whispered as a game that's a benchmark for old-school difficulty. All successful games want to be a benchmark for something, whether its visuals, writing, gameplay etc. It does half your marketing for you.
Etrian Odyssey doesn't have broad appeal at all, it's the definition of niche, but it does have a tiny bit of that Dark Souls DNA of having a rep for tough, rewarding, old-school gameplay. It's a great update of Wizardry, but I wonder if the anime art severely limits what could be a great resurgence of the turn-based dungeon crawler overseas, alongside Legend of Grimrock etc. Still, at least it's cheap to make, focuses on gameplay and the minimalist storytelling leaves the player to come up with their own characters. I much prefer that in RPGs, even if its unusual for a JRPG. Gameplay is the focus here, but its kind-of put itself in a corner with its art style. Consider how many people played FFXIII and then leapt online to complain about it, compared to the portion of those talking about EO. The visuals put some people off, but if it can get people to try it they get hooked. Disclaimer- personally I love the art, it was my favourite new IP last gen.
Nobody's mentioned Monster Hunter yet, I don't know if it really counts but the online community for Tri in the EU was just awesome, I don't think it sold too badly either.
Pokemon- I missed out on the craze by being too old in 1997, but it's obvious that its not just a fad- the game apparently has a really addictive system of progression and party building and I was always surprised to find that other older gamers played it just due to that.