Apparently they expected selling more than FFXV
The last numbered instalment, Final Fantasy 15, remains the series’ fastest-selling entry with 5 million units shipped and sold digitally in its first 24 hours alone. This was across multiple platforms, however.
When that only other platform was Xbox, though, I doubt that total remotely compared to PlayStation sales.
I honestly think it’s just lack of trust in the series after 15 along with the economic times we’re in, where people don’t want to spend money on something they’re not 100% confident in. It also didn’t get the same media cycle as 15, and didn’t have strong nostalgia value to coast on like 7 Remake.