Why did the Galaxy Z Flip apply in-folding design?

For foldable devices like the Galaxy Z Flip, they can be categorized into 2 types (in-folding and out-folding) depending on the way the device folds. For its Infinity Flex display, Samsung decided to implement an in-folding design in which the main Flexible Ultra-Thin Glass folds inward. 

Flex displays by their nature, are vulnerable to damage from external shocks and scratches and the out-folding design exposes its display at all times. In-folding technology, meanwhile, offers the most protection for the display from scratches, damage, or any accidental touch commands.