At this point it's all just for money. They can create new fancy character models and do some work on gameplay, but it didn't need to happen. It's the same thing that happened with the Spider-man remaster. Why did they have to change the character model? To me, that just screams cash grab, because I don't think people care too much for another HD upscale of a game that already looked damn good even on the PS3.
Yeah it's nice to get an HD upscale/remake of a popular game, but I feel like it's way too soon for a lot of games. It's just recapturing the glory of the game as much as possible. Once a PS6 comes out, who's to say they won't make yet another remaster of the first game?
They could also be using this time to develop a new game in the series, or a new franchise even. I know that a lot of these remasters are tossed to smaller studios, but still, I feel like those smaller studios could be tasked with making something they really want to make. That's another thing, developers tasked with making remasters and remakes, must hate it, because it takes them away from developing brand new ideas.