Personally I would never write in my Bible it seems kind of wrong to me so I get your question and what you feel about being taught not to. I feel it’s disrespectful myself, but I guess it’s a personal thing. For me it would never work, cos the Holy Spirit moves me differently at different times when reading my Bible. I keep a prayer journal and write in there the outcome of my prayers, prayerful reading of the Bible and any mental prayer reflections that come to me so I don’t need to write in my Bible even if I felt so inclined which I dont. I include the Bible passages when it’s from readings and it is dated so that I can go back and compare over the years how things have changed.