True, not everything is a grind though things that are less enjoyable tend to end up called grinds because the player is not having fun doing it and feel like it's taking up too much of their time they could be doing other things.
But let's flip the question around: why should anything have to be a grind? I'm not talking about just handing out things for the asking. There should still be effort involved. But is it really necessary that something require dozens if not hundreds of hours of time investment? It's a game, not a job.
"Well if they don't want to spend the time, then can skip the reward." Yes, I agree with that.
There are a lot of things I dislike and so I skip doing them. I did one ARR relic and one HW relic for the story. I totally skipped the SB relic because I hated Eureka from its release and while I did end up doing it in ShB with my FC just to see the story, I ignored the relic grind. I started on the ShB relic, got the first two upgrades done, decided I didn't enjoy Bozja any more than I enjoyed Eureka and quit it. I haven't really started on the EW relic yet because I've been focused on doing other things but for now I expect I'll get at least one done through the 6.35 content because I get to choose what I do. It won't be forcing me into content I don't enjoy. We'll have to see what the remainder of it is like before I can say if I'll finish off this one like I did the ARR and HW relics.
"Grind gives a sense of accomplishment". I'd respond with "wouldn't spending the time on something meaningful in life give you a greater sense of accomplishment?". I went through the Pteranodon grind in Shadowbringers. Now I have a mount I rarely use. I'm happy that I met a goal I set for myself but I don't feel like I'm a better person for having it done it. Some of the things I'm working on in real life right now that have taken a fraction of the time are giving me a real sense of accomplishment in comparison because they are leading to life improvements for myself and for others.
I think people put a little too much emphasis on what they do in a game at times. Why is probably different for each but I fear for too many it's because they feel incapable and powerless to achieve what they want in life so they turn to games to feel capable and powerful.
In the end, games should be fun and not feel like your time is being wasted. In other games in the past, players have ended up feeling that their time was wasted with the long grinds for rewards that were useless soon after. SE seems to be trying to tiptoe around that pit to find a spot that leaves the majority at least content with the result. They do listen to feedback and do make changes in response to it on occasion. So for this grind they listened to players who hated being forced into specific content in Stormblood and Shadowbringers. They've given us a grind where the player gets to control how much or how little effort they put into it.
And of course those who prefer a grind are now complaining because they took the easy path to completion instead creating a grind to their liking.
The devs just can't win with us.