I think it made sense for 7. Midgar was the most interesting set piece and a ton of stuff happens there. But it’s only like 10% of the game.
Then you collect side characters like infinity stones and to through a bunch of their individual stories.
Then the actual story happens.
Also, 7 is popular enough to support the split up.
This doesn’t make sense for 9. Also, isn’t it supposed to be a 1 for 1 remake?
I don’t think it even makes sense financially. There’s not really a first part for people to get excited about compared to Midgar in 7. 9 is more of a full package game.