Thick Thighs Save Lives
NeoGAF's Physical Games Advocate Extraordinaire
During the latest Final Fantasy XVI broadcast, the game's producer, Naoki Yoshida, revealed that the title was initially planned to be on two discs. However, just six months before launch, the team managed to barely fit it onto one.
This was highly desired since keeping the game on one disc significantly reduced manufacturing costs and avoided delays in polishing the overall experience before the title went gold.
While a PlayStation 5 game on two discs sounds far-fetched, it's not exactly new. The upcoming Final Fantasy VII Rebirth is confirmed to be featured across two discs, so it's no surprise that Final Fantasy XVI almost embodied that identity.

More at https://noisypixel.net/final-fantasy-xvi-almost-2-discs-1-disc-half-year-pre-release/