Long ago folks baked loaves of bread at home or bought them whole from a bakery. At some point, it became possible to buy the bread pre-sliced. The Wikipedia article on Sliced Bread describes the history of bread slicing and how the expression "The Greatest Thing Since Sliced Bread" came about. Apparently sliced bread was a wonderful breakthrough. Today only artisan bread is sold whole.
I bought my first loaf of unsliced bread just a few years ago. I really liked it!
First of all, it was not at all difficult to slice the bread with a proper bread knife. And I could make the slices any thickness I desired. I usually made them as thin as possible. For small dense 100% rye bread, that's less than 1/2 cm (about 1/8 inch). I'd allow for nearly a full 1 cm for more porous, airy loaves. Compared to sliced bread, my slices are 25% to 50% thinner.
Second, sliced bread gets stale more quickly. A whole loaf has a crust to protect the inner portion. Once it's sliced, that protection is gone. I keep my bread wrapped tightly in an intact plastic bag and refrigerated, so the loaves I buy last a few weeks. (I don't eat much bread.)
So every time I slice bread, I smile and say to myself, "Unsliced bread is the greatest thing since sliced bread."