I'm from the United States and I have recently discovered that I don't pronounce the T as a soft D as other Americans do. Neither do most of the people in my area or my parents. I pronounce the word "butter" like someone from most areas of Britain would, I don't pronounce it like "budder." Other than the pronunciation of this consonant, my pronunciation aligns with the main American pronunciation. I was wondering if there is some kind explanation as to why the pronunciation of the t hasn't shifted to a D in my area? I live in the Southern New Hampshire by the way.
Maybe you have (or have remnants of) the so-called Mid-Atlantic Accent. https://www.atlasobscura.com/articles/how-a-fake-british-accent-took-old-hollywood-by-storm