It's called vertical integration, lemon

A folding display feels so... anti-Apple. The crease in the middle of the screen and reduced durability go against their general perfection and the user choice of a different form factor is not something they usually do. Plus, half the reason I would buy a Samsung Fold is so that I can run two apps at once side by side and more space for floating apps, but Apple has never had such power-user features. I will be very surprised if they actually release one.