I feel the same as you. I'm guessing you refer to the turn based ones rather than action? It could just be it never really aged well. I try to stick to short rpgs. 10-20 hours max. People complain about a rpg of that length but i'm quite happy with a length like that.
I'm mostly referring to classic turn based JRPGs on the SNES, PS1 and PS2. I 100% agree about the shorter JRPGs being more appealing which leads me to part of the reason why I think my interest in them has steadily declined.
I graduated high school in 2005 and started college that same year which really decreased the amount of time I had to devote to playing them. I remember starting about 4 or 5 different JRPGs my freshmen year and being interrupted in the middle of playing most of them for weeks or months, and by the time I had free time again, I just couldn't get motivated to start playing them again. I then realized that I wasn't having a ton of fun with them when I was actually playing them either.
Don't get me wrong, there are still excellent JRPGs out there that I enjoy, but most of them I just can't get into them, most of the time because of cliche anime-like characters, boring or confusing stories, bad english translations, or some other crap that just turns me off to the game. Someday, if I ever find myself with a lot of extra time on my hands I may make a honest effort to get back into the genre, but i'm worried that the content will prevent me from loving the genre as much as I did when I was 13 or so.