As others have mentioned, there are a ton of off-the-shelf solutions that would have been more than adequate for this. My question is, why didn't he go for any

As others have mentioned, there are a ton of off-the-shelf solutions that would have been more than adequate for this. My question is, why didn't he go for any of the existing solutions when setting them up would've still been faster than rolling his own DB-in-a-JSON-file solution?