The Zenless Zone Zero community has been doing a bunch of arguing, so I wanna go over why interest may have dropped off as much as it has, at least in my opinion. Keep in mind that I am still playing and enjoying the game, but for who knows how long, I guess we'll see how Version 2 plays out.
Point 1: The Characters
The first is the most obvious, and that's just the Limited S-Rank characters are really boring. They look exactly the same. When people get excited for a character, it's usually an A-Rank or they literally came out in 1.0.
People care more about the Panda than they do Yixuan. People cared more about Big Daddy than they did Caesar. Billy was really popular, but he's also the worst character in the game, so screw you I guess.
Just going off vibes, I still see Burnice and Ellen floating around out there, but I think a part of that is just because Ellen is a super weird looking character. They went a little outside the box by creating a shark girl wearing a maid outfit, but it paid off for a lot of people.
The point being, the basis for creative, fun, and interesting character ideas are there, they've just been severely limiting themselves because the developers think those ideas for characters have to be sexy ladies and nothing else. That can result in some good characters, but only sometimes, not all the time.
If you don't believe me about the Limited S-Rank characters being dull, look at how many people thought Ju Fufu was an A-Rank when they first saw her.
Point 2: The Casual Player
You see that chart there? This represents where Hitpoints started out as in the beginning of the game, and the pink dot is where it will be after Yixuan comes out.
Now, you could make the argument that this is just the natural result of there being new Drive Discs being added to the game, as well as new W-Engines like the Marcato Desire. They've also made it so instead of just one character being able to use an Ultimate, now the entire team can use their Ultimate, so now the game needs to be balanced around this new damage potential.
The issue with this is in Zenless Zone Zero, is it has gone from being an easy game for everyone, in fact it was considered too easy in the beginning, to becoming more difficult for people who haven't fully committed to optimizing their teams. Hitpoint inflation is also just the laziest way to implement a difficulty change in a game, let's be real here.
They want to keep the fanbase they've already created, but by continuously making the endgame harder with every update, how do you then onboard new players by doing that? What is going to incentivise you to keep playing the game, when it feels like the endgame is just not possible for you?
Point 3: The game is boring?
This next point is going to be very subjective, but there's a lot of stuff in Zenless Zone Zero. There's arcade games, there's dating mechanics, but how interesting is all of this? Are these things that you want to keep doing over a long period of time?
A good example of this was the TV Mode. People hated it, they felt that it took too long, so they got rid of it completely. I'll let you form your own opinion, but this is just something that gets on my nerves in certain game series' sometimes, that just because it wasn't done perfectly the first time, doesn't mean that you should just throw it out entirely.