It's probably related to how we read and write. Top down, left to right. Rows are the entries, columns are attributes. Your list will potentially grow forever,

It's probably related to how we read and write. Top down, left to right. Rows are the entries, columns are attributes. Your list will potentially grow forever, whereas the attributes are typically fixed. Your width is typically fixed, but you can continue writing top down and continue on a new sheet/etc, as you add more rows. It just makes sense with how we typically organize information on pen/paper.