Are these files all formatted in the old tv format? It seems to be the same for this anime series everywhere. I would've thought it was originally filmed in 35mm format and could later get released in the 'modern' format if it was originally released in basic box tv format?

Yes.  Artwork is drawn to the aspect ratio of the intended broadcast medium.  It would be a huge waste of time and money to do otherwise.

Think of it this way: if you have the original drawings or cells, you can take better or enhanced pictures of them now (resolution), but you can't change the shape of how the artwork was drawn without loss.  You can distort it and make fat people, or you can zoom in to fill the top and bottom of the screen by cutting of the side edges (cropping).  Most people don't care for either of those solutions.  You can try either in your video player and see what you think.  In some remastered BDs there is some cropping or distortion or both.  Dragonballz, for example.