Platform exclusivity is definitely hurting FF in the grand scheme of things, there is no question there.
But on top of that, FF is just a very messy franchise to figure out from outside if you are not part of the fanbase already.
In terms of gameplay and structure there is no clear identity. Any one FF game could be anything in terms of how it plays and how the game is presented to you, which is fully against how you'd attract and build a mainstream audience for your brand. If your average Joe has no idea what the next game is gonna play like or how its core design will be (will it have different playable characters? Will it be OW? Will it be linear? Will it be action? Is it a hybrid? etc) they are not gonna care about your franchise.
But that's assuming that said average Joe has even been able to get into the franchise in some way. Even if someone has heard about FF7 remake projects and is curious about it, this is still a shit ton of fluff that would confuse the hell out of them if they don't have their finger on the pulse.
Your mainstream, 3-4 games a year player that maybe gets into stuff like Spider-Man, Horizon, etc as well, is probably not gonna parse through all of this to even see what's this FF7 game that they might've heard about somewhere.
That's one part of the problem, the other part is that even if you manage to get that kind of players into one of the entries, which is something that XV likely managed to achieve to some extent, when 6-7 years later your next game comes around and said player manages to catch it between all the cross media projects, spin-offs, remasters and smaller FF adjacent games, it might be completely different than what they were hoping for after playing XV and liking that game.
All in all, there are a lot of things that are working against FF building up a bigger audience base that it already has.
Edit: I just remembered I wanted to talk about Yakuza and Persona as well, since those were brought up in the thread. Those 2 are great examples of not only doing it right in terms of releasing day 1 on many platforms, but also not being too confusing in terms of what the player can expect from them. Persona has a bajillion spin-offs in different genres with different tones for different audiences, but the difference here compared to FF is that when you see just "Persona 3" or "Persona 5" on the cover, you know it's that long turn based JRPG with social sim elements and a calendar system.
Same can be said about Yakuza, to a lesser degree since they just went through a name change here, but still, you know what to expect from a Yakuza game in terms of structure and if you have Ichiban as the main character you know what's in store for you gameplay wise as well.
FF doesn't have that and that's hurting it, regardless of how people feel about each game doing everything from ground up.
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