First some definitions or my understanding of terms.
JRPG - Story heavy, narrative driven games originating mostly from Japan with anime tropes and featuring turn based character battles commonly
Core gameplay - The main gameplay element of a game, for example Dodging, rolling and spacing combat in Elden Ring, Monster Hunter. Character placement, team builds, XCOM, TRPGs
Sub system - Mini games or the social systems in Persona games, a secondary gameplay element that is different and unrelated to core gameplay
I've enjoyed Yakuza Infinite Wealth, FF7 Rebirth and Persona these few years which led me to think that I enjoyed "JRPGS" so I booted up old "Tales of" game (action battle) and am having a hard time pushing through
I then realised that the JRPGs I've played have a lot of investment into sub systems, Yakuza basically being a collection of minigames polished over several series. FF7 adding even more mini games than the original in a 1/3 installment and also having a non turn based system and Atlus' games having a large chunk of it being a dating sim on top of its flashy UI for the turn based battles.
I think the core reason is that other gameplay mechanics, from driving to shooting to RTS to combat have high skill ceilings such that people playing CS can transition to Overwatch and then to Marvel Rivals and maintain their level of training over years. RTS have high skill floors for PVP. Meanwhile for single player RPGs without deep builds and customisation, you should be able to complete the story and endgame with grinding or items or clever builds. The first 2 being the easiest and least 'fun'
This has led to mainstream JRPGs needing sub systems to support the price tag while CRPGs like Baldurs Gate 3 have builds and branching stories to make it fun and replayable.
On the other hand Dragon Quest 3 hd-2d remake sold like gangbusters so maybe I'm off on this
From my point of view, you've got it wrong, but so do many developers. A good JRPG is all about resource management. Your HP, MP, items, money and the balance between these and your EXP and equipment. Combat is simply a drain on your resources up until the final boss, which should require more strategy. This needs something akin to a dungeon without constant healing and money being a thight resource. Once you're in a dungeon, you should either be prepped or doomed.
You mostly see this done in dungeon crawlers, think any Etrian Odyssey game for example. Persona 5 goes for the same thing, as do most Shin Megami Tensei games.
Most modern games, however, are overly lenient with either money or healing. Often times, combat is easy enough to not even drain your resources. That's when endless grinding becomes an option. Once you've destroyed this balance, you need something else to keep attention and that's where I think your observation comes in.
Is this a modern/old dichotomy? Playing through Metaphor right now, I agree that they go with the old-school dungeon crawler approach, but Chrono Trigger and Final Fantasy VII are definitely not modern, and I don't think they'd fall into the same bucket.
Not entirely, however, I feel as though proper resource management got less common over time. While the ideas are still present in modern games, they tend to be easy enough that most resources can just be horded. Most people don't even use consumables nowadays. Games are seemingly balanced around ignoring entire systems.