hmm aren't most JRPGs played out like that? I mean aren't most other genres (ie. action-adventure, shooters, etc.) played out like that as well? The comparison you draw to WRPG is valid, but why can't I like both? They're just different types of RPGs, I can say games like Mass Effect/Dragon Age/Witcher all have some bland cliched stories as well. It's not like we didn't predict the ending for those games as we played. AS for this whole characters/anime style-thing, you have to remember who the target audience is. In Japan, that's the way characters are! In the PSone era up until the closing days of the PS2 era, when Japan was still the dominant in the gaming world, Japanese companies were making companies for JAPANESE PLAYERS! If the game happened to be a success in the west, that's just icing on the cake. It wasn't until the Western market start mass adoption of the consoles did Japanese companies start gearing games towards them! So it'll take some time for the whole "anime-style" thing to clear away, but one day it will (Final Fantasy XIII has already taken some leaps in that area).

Back to the topic as to why the Final Fantasy series has mass appeal, It's the opinions of the millions and millions of people sinking their money into it. Even today there is NO WRPG THAT HAS COME CLOSE TO FINAL FANTASY IN SALES! Everything from the story to the characters to the bredth of how engaging the system can be is what seperates Final Fantasy (and most other JRPGs) from the pack. I can't really answer your question in a traditional sense for an answer, but WRPGs and JRPGs (like FF series) are just different experiences and people play whatever they want to, whatever they think is more fun and engaging.

@Shaibana
No He's not talking about open world games (GTA, Assassins Creed). He's talking about games with branching stories and large overworlds where you "direct" the control of the game (mass effect, dragon age)