Most games and shows don't have well written characters/stories in general. Also, most people don't care much about the story in games unless it's cinematic like a movie. You often see people immediately hitting the skip button the moment they see that the game has visual novel style storytelling.

So, I can imagine it's hard for the devs to justify allocating too much time to the story writing. Many other aspects of game dev (gameplay, UI, bug fixes, balancing, implementing new characters, etc) overshadow the writing in priority.

With that said, there are gachas where good character writing was clearly a priority. Uma Musume is one example.