Because you'd be fingering the motherboard if the screen would be flexible.

We have the technology to make immortal screens, it's just that none of us can afford it. Diamond surfaces are achievable and are virtually immune to scratching assuming you have a cash fountain you no longer need.

Or, assuming you can live with a less-than-one-inch screen. Watches have very-very-tough screens since forever.

Tissot used to sell a sapphire screen with touch for a watch, IIRC. <Google>. Here we go. "By simply pushing the crown and then touching the tactile crystal at different positions these functions can be activated. Touch the screen at two o'clock and your current altitude appears on the digital readout. Touch the crystal at six o'clock and the hands move around into position to become a compass". About a thousand USD, before you ask. ~30 mm diameter, before you ask.