Why are JPRGs called JRPGs?
Marketing.
Seriously, though, there are differences between what W/C/RPGs try to do and what JPRGs try to do.
For the most of their existence, western made RPGs tried to emulate TTRPGs, which means you create your character, you make character progression choices, at least partially (since, unlike something like RuneQuest or GURPS, even D&D never gave you completely free character progression, given that some things are hardcoded in class/level progression), your character acts toward the world in a matter that tries to emulate RL (AKA "everything goes", so everything can be tried), and world reacts back as close as possible to RL, which translates to any problem can be tackled from different angles, with different short/long term consequences, both for character and world.
Of course, the amount of western made RPGs that actually pull this off is 0, but that is, more or less, a theoretical ideal. In practice, they are orders of magnitude more constrained by medium, since you can't code or predict everything, budgets, no matter how big they are, are limited, and there is no GM to improvise and adjust on the fly all the wheels that are in motion, so even most lauded western made RPGs, which check a lot of those boxes, are far cry from that ideal.
Now, my knowledge of JRPGs is very limited, but from what I observed, they tend to be focused on telling (fairly) preset story with (mostly) preset characters. In TTRPGs this often falls under "railroading" or, in extreme cases, "failed novelist GM" approach. Not saying all JPRGs are like this, just like there are quite a few western made RPGs that are more akin to this (and thus pretty much fail at being true to RPG core principles), but JRPGs tend to generally be way more constrained. Which is quite odd, given that JPRGs began as a mix of RPGs and visual novels, and from what I've heard (not really got into it yet thoroughly), there are plenty of visual novels that are very open-ended and have branching stories.
This is a very fun video from one of the most recognizable people in TTRPG scene these days, Matt Collvile (who worked in both tabletop and VG industry, started a YT series "Running the game" some 7-8 years ago to give advice to folks who want to be GMs, and whose MCDM productions garnered around $10 millions combined in crowdfunded projects), on The Sandbox vs The Railroad.
Another one, discussing Railroadng, Agency and Choices (more to the point and with better distinctions and advices)
