There's another point I'd like to bring out, I see games like Final Fantasy VI (3 if you are old enough) and Chrono Trigger have gotten mentioned quite a lot, so maybe and just maybe the JRPG genre actually has remained the same. but It's us that have changed. Allow me to explain.
The JRPG genre was never a mainstream type of game, even when masterpieces like FFVI, Chrono Trigger and Secret of Mana were coming out left and right It was games like Doom, Donkey Kong, Mortal Kombat and Street Fighter were all that kids were talking about. there were great games like FF5, Chrono, Secret of Mana, Xenogears, FF Tactics, Suikoden etc, but they weren't breaking records in sales, heck, they weren't even getting the best reviews so Its's not crazy to say that JRPG was more like a cult, very devoted fanbase but not in large amounts.
Secondly, if we're able to remember all these games mentioned above I'm going to assume that we are not 11-12 year old kids, most of us are near our 20s, my theory is perhaps we just dont have the patience, time and dedication an RPG game requires, I mean I put in over 130 hours into my FF6 characters, I did all of Chrono endings, I just dont have that much time anymore, as a matter of fact somedays I dont even get to play, therefore Its hard to stay tuned in the game's story. I have talked to my friends they feel the same way. thats why most people prefer short-story games, very linear, easy to remember firts person shooter types. I still play JRPGS but I just can't get too deep in them now a days. anyway thats just my opinion.