Here's an article about Sea Island Cotton, a well known top of the line material. Long staple cotton is softer, the texture gives it a nicer feel on the hand. Zimbabwean and Egyptian cotton also has a long staple. Varying qualities are often linked to growing conditions & environment. Obviously a noticeably softer fabric that can only be batched in small quantities is going to cost a ton of money and those costs multiply through production, wholesale, and retail.