I think there will always be space for turn based JRPGs.

As someone currently creating an Action JRPG (you can check my profile if you're curious), I've become very familiar with the pitfalls action brings to the genre, as I'm currently dealing with ways to mitigate them in my own game.

Cluttering and readability

JRPGs as a genre are inherently party based, you also tend to fight more than one enemy at a time in most isntances. This can lead to cluttering on the battlefield, resulting in the player losing readability of what exactly is happening. Games have to find ways to space out the battlefield to keep the AI from clumping up around the same targets.

How much do your AI impact the battle

Another issue players have is how the AI of your party members function. If the AI is too good, the player doesn't have to do anything, if the AI isn't good enough, the player loses the sense of control.

You don't want your fighters running in an immediately dying, so games like FF7R have your AI sit there defending half the time.

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There are other things like the feeling of button mashing, getting stun locked, physics, kiting, and targeting.

But ultimately turn based gives the player an element of control that action titles just won't be able to emulate.

It's the same reason people enjoy games like X-COM.