Persona 5 and Royal is a bad example as both of those games are good and different enough to justify paying twice. The correct example is SMT V and VV.
I disagree. I love both of them, but I gotta say P5 is only fun once. It is way too dialogue heavy for a 80h game to replay and literally every side activity is boring on a repeated playthrough, hence I'd never have gotten to the actual Royal story content if I had played all of P5 initially. Yes, I could skip through most of it, but at that point I'm only playing a worse SMT with way too many interruptions and would potentially skip some changed stuff. SMT V on the other hand I see myself replaying anyways, should there be enough new stuff I'll go for VV. It's just pure gameplay goodness.
I don't own P3 Reloaded, but is this sort of like the additional content that usually comes in Persona 4 Golden and Persona 5 Royal? Shouldn't this have been included in the P3 Reloaded release?
Episode Aigis (or The Answer in the west) was an expansion/epilogue to the base game. (In)Famous for its focus on combat and sparse story content.
The original release was pretty long (about 30 hours, I think) so I guess they thought it would be too much work to add it to base remake? Or they just wanted money, I dunno. It's Atlus. They have a... special approach to game development.