That is a valid question. When I started with a Hasselblad I was just starting my business. I shot exclusively color portraits. Studio portrait photographers generally buy ready made frames, folders etc from our suppliers. The range of frames is extensive and high quality.I agree with you, people love this format. Personally I cant understand why someone like Michael would buy a square format and almost never print square.
Unfortunately, they as well as the folders for small prints only came in 4x5, 5x7, 8x10, 11x14, 16x20, 20x24, 24x30 etc. never square.
So it is a habit that has stuck with me and I rarely "see" square.