I've got a few things to say on this.
As for FF7...Uh. I've been playing games for many years (and from many ideas prior), and this whole idea of games of today being flat and simple is frankly pretty off base. Games have by no stretch gotten worse, and games with deep stories/characters and hard difficulties are still being made constantly. The state of gaming today has absolutely nothing to do with why there's no FF7 remake. It's because it would take effort.
That's the only reason. They are fully capable of making a remake, and they have the time, money, and demand to do so. But they don't have a reason to because they're doing fine, and they know that it would bring in the truckloads, possibly more than even a new Final Fantasy iteration or Kingdom Hearts 3. It's easy money for when they're in a tight spot, so there's no need to do so just because people want it.
As for the games...you know Square wasn't out on their luck when Final Fantasy came around, right? Sakaguchi was, and that's why he made the game, and if it didn't do well he was going to stop. That said, Final Fantasy 7 through 10 weren't exactly saviors for the company. After 10 was released, they were still in a tight spot and that ultimately led to the creation of Square Enix, since the latter company was also in a tight spot. Final Fantasy I wasn't particularly known for its story (since that was pretty bare bones), either, it was more the adventure that it spawned that people remember. Final Fantasy III is where the series really gained ground, though, as its rival Dragon Quest was beating its ass every which way.
And as for 12, why wouldn't they? It's the only other one that makes sense to do an HD remake of. An HD remake. HD remake =/= remake. They don't completely rebuild the game from the ground up with groundbreaking graphics and the like, they just sharpen up textures, possibly music quality, and cutscenes to work in HD. Hence why they're easy to make and why we saw one for FF10 and the Kingdom Hearts games. It only makes sense, moreso than a FF7 remake would, really. Plus, there's demand for it.
As for that bit about Squenix not being able to make good games anymore, you realize that Final Fantasy XIII is made by different people with very different ideas and ideologies than the previous games and that's why it's so different, right? Same for XV. And it hasn't been all bad. Lighting Returns was a lot of fun, my favorite XIII entry, Type-0 was a nice entry, Agito's still a thing, and XV's getting good reception, far more than when it was announced.