Because it was pointless.
The first episode starts: during this you are being interrogated for the Phantom Theives latest heist and everything is a flashback. You're a troubled teen who has gotten in trouble with the law and been forced to move in with a caregiver, you go to Shujin Academy for school, you end up in a weird dungeon like place where you are captured by the ruler of the dungeon a teacher from your school, Kamoshida, who is an abusive phys ed teacher and coach, you end up being tortured and suddenly release Arsene, your 1st Persona. To make that a comparison to the game, you get through the first hour and half or so. Well that's not so bad right ?? Just an animated version of all the talking and activities you do in game. The issue between the animation and the game is interactivity. I choose what I want to do in Persona 5, how I want to approach things, what I want to do each day, when I want to progress in a dungeon towards changing someone's heart. Taking away my ability to battle in dungeons with the potential to lose and have to start over, to take away my ability to use the cool abilities Joker or his companions have, to take away how I build my relationships with these friends, what Persona's I want to kill to make new ones or ones I want to join me.......
Basically, to take away PLAYER CHOICE is what the animation does and it kills it a little bit. It makes the anime pointless. I know what is going to happen already and I did it MY WAY, that to me is what is most important, I got to where the anime gets to but my way. I think that without player choice that Persona loses a lot of its charm, it becomes just another anime to watch then, it's just a random story to people who've never played the game. Sure, if you never plan to play it and you watch it, you may love it and some fans may love it too but I saw it as something made for the games fans......something made for the fans that missed the mark with how it was essentially a fancy done recap.
Thing is, a lot of the big instances in the game have actual anime cutscenes to them already; done by the same people and the same studio that did this show. Top off that even the regular cutscenes character models are so well done that any animation isn't needed to spruce it up. So the anime cutscenes IN GAME are already icing on the cake and they didn't need to be their own show. Having the anime is an awesome idea absolutely but when it is done for a game that has anime cutscenes built in with regular cutscenes and being done in spectacular fashion it's hard to see it as anything but pointless. Fun, yes, but not needed. Another thing that hinders this anime is that a lot of people played Persona 5 in English, I didn't so I recognized all the voices, but to those that have played and beaten the game and come to love all of the crew's English voices will be thrown for a loop and it detracts for them as well.
If there is a positive takeaway from this, the Persona 5 Animation was incredibly well done, and still maintains the Persona feel but the lack of interactivity haunts it. Really haunts it. If anything what they should done is to just have stuck with the Persona 5: The Daybreakers, which was a single anime episode that came out pre-North American launch of the game, and went over how all of the crew in the Phantom Thieves does their job to take people's hearts and confess their sins. It was a well done, one-shot anime that was a good introduction to Persona 5, you were able to go into the game without it but with it you had an idea of what they do. It was just perfect and I didn't think they would do more, nor did I want them to do more.
I can say the same thing being pointless of the other Persona anime & movies but to a lesser extent.
If you are a Persona fan, give it a shot but just know you'll be getting exactly what you played but in anime form and every choice you as the player made isn't there so it is very streamlined. Or if you wanted to finish Persona and just didn't have the time or just couldn't do it, I suggest picking up the game and trying again first but if not and you do want a quickish version of the story then watch this.
Otherwise I stand by my statement,