That's a major part of it, certainly. The synthesis system is meant to be a big part of the game. The expanded Mark system, too. I actually planned out a ten-Mark chain - a plotline that has the same number of story battles as Chapter 1 of FFT - towards the end of the game that covers a lot of backstory, side plots, and endgame equipment acquisition.
But also, things have been shuffled around since the release of Chapter 1. Items and abilities have been re-sorted, the text has been redesigned to counter issues like being unable to load an entire section at once, I'm pretty sure the ASMs have gone through some alterations to allow Jot5 to run on actual PSX consoles...
While everything could certainly be stitched together as is, I don't think anyone here really wants to do that now only to do it all again later.
But also, things have been shuffled around since the release of Chapter 1. Items and abilities have been re-sorted, the text has been redesigned to counter issues like being unable to load an entire section at once, I'm pretty sure the ASMs have gone through some alterations to allow Jot5 to run on actual PSX consoles...
While everything could certainly be stitched together as is, I don't think anyone here really wants to do that now only to do it all again later.