The main problem is not Unity, it's more the game aiming to be, well, game. It doesn't sound as terrible thing. But don't forget that half of this "gaming" community is just looking for quick fap (and would be better off with regular porn), and even those that don't, seem to prefer VNs. And I get it, I'm leaning to that too. Partially because I'm getting lazy, I guess. But it's also affected by development model.
I'd love a game like this, with free roaming, stats grinding, and everything. But ideally a game, as whole game, not tiny piece now and then. The real fun is when you get into it and keep going. But you can't do that when you get only a bit at time. You hit the end before even warming up. A month later with new update (and that's usually unrealistically optimistic) you barely remember what you wanted to do. It sucks. And it sucks with VNs too, only with them it's slightly more palatable, because you don't need to remember too many details, just vaguely what the story was about, and continue reading.
It's nothing against developer personally, I understand that a single person or small team funded only by donations don't have a choice. But it's quite unfortunate and doesn't help with getting support.
And Unity vs. Ren'Py, yeah, that's a factor too. But it's the gaming community being stupid. Ren'Py is wonderful invention, it makes development more accessible to people who wouldn't be able to do it otherwise. It's a blessing, but also a curse. It's the vanilla of development, it works fine, everyone likes it, you can't go wrong with it. But it doesn't mean we have to get stuck with it forever. Doesn't anyone want to see something new? More interactivity, new interesting mechanisms, anything? Admittedly, the water gun minigame is not the greatest example of such thing, but it has to start somewhere.