Doesn't mean they necessarily have to be the most well written stories, but they bring forth some really relevant real world issues and questions that give me valuable insights on life and think deeply about the issues that are portrayed. The characters' relationship dynamic also plays a huge part portraying these issues. Note that most of these are completely smut-free or no smut, pretty obvious why
Note: Someone asked me why I don't just go read philosophy instead of searching for it in BLs. I'd say, gayness is a great message