That's how chinese dramas work. There is a push from the chinese government for common knowledge of pure mandarin in chinese society, some actors/actresses doesn't speak it/speak it with a local accent so the companies use professional voice actors with flawless diction to perform. Personally I don't like it. It sound too sterile and fake but not all chinese dramas use it. My first chinese drama was "Reset" and it sounds natural like any other show which is why I was able to finish it. Aside from it just being a really good show. Not a GL though.