I was thinking about something like that, which is fine for…

I was thinking about something like that, which is fine for a platform like this, but that's impossible to stitch all together on the blockchain since it's impossible to link to transactions that haven't yet been made. A completely separate transaction would have to be made after the fact that points to each uploaded section.
That sounds cumbersome to do when the blockchain can be used as an immutable Internet Archive or Project Gutenberg for plaintext documents. This is why I think it's important to have the whole thing in a single transaction to easily do a Ctrl+F if you need to quickly look up a passage.
I'm sure there are plenty of other use cases, but that's my current thought process for this issue in particular.