I’ve had two iPhones without cases for 10+ years I’ve cracked a screen twice, doesn’t exactly seem like a pressing issue
Each screen replacement cost me around $75 to replace DIY.
In exchange, I have 4 3-6 year old phones that look and function as new. If you hold them just right you can see fine scratches in the light, but at a casual glance, they appear unblemished. That would not be the case if the cases were plastic. I also get the convenience of wireless charging (not possible in metal cases).