It is more about their ability to make a half ass port for a next gen console they most likely have not really bothered to learn the ends and out of. They might do a port later but considering the ports on the handhelds they have done are using mostly the same game engine as the PS2 entries, I feel it is a safe bet they have been slow to adapt to the new tech, hence one of the reasons why Catherine was created to serve as the team's intro to using the PS3 console.

The poor reviews line comes from them, in the hypothetical situation they actually did do a PS4 port of the game to coincide with the PS3 one, it would most likely not make use of any features or even be high quality in graphics or sound to take advantage of the PS4 hardware. It would feel like a cheap PS3 port to make money and considering Atlus gets reamed for their questionable DLC as it is, the last thing they need to do it mar their reputation with a cheap port or worse, pull an SE and promise a game on one system only to turn around and delay it so they can release it on a new system properly. It just seems to me like a waste of time to try to expand a project in its closing development days to incorporate another console release and unlike SE and EA who often have hundreds of people working on games, Atlus is pretty small and really doesn't have the resources to pull it off in a way that would satisfy the fans. Hence why I would bank on it getting poor reviews, especially since games like Disgaea are often criticized by fans and critics alike for sticking to a graphic style that is two generations old now, in the face of games that have really improved on the expectations of sprite based games.

I actually expect P5 to look like a PS2 game myself. Atlus is not exactly a sensory overload specialist like SE or Konami and they have proven they don't really need to but in the early days of a console cycle, people are often expecting games that really show-off (more like verify to themselves) why the console in question is worth the money. So I don't think a port is going to make anyone happy if they can't bring something to it.