Supple leather is just leather that is soft and pliable, it's still just cowhide, but would be treated differently at the tannery to make it softer and more pliable.
To get the wrinkled effect in a factory setting, each one of those stitch lines is run through a shirring machine that gathers the fabric and sews it to something that doesn't stretch to hold it in place and create wrinkles. Making wrinkles may seem like it should be easy, but it's not. In an upholstery shop that won't have a dedicated shirring machine, the wrinkles are created with elastic and then sewed to something that doesn't stretch to hold the wrinkles in place. The amount of wrinkling has to be planned ahead of time so that each section has the same amount of wrinkling.
No one lives forever, the trick is creating something that will.