Comment by zamadatix

I think the average person wouldn't run into a meaningful problem without a case, maybe a light scratch or two somewhere if they looked closely, it's just the idea they might need a case that leads them to use one. This is probably even more true of screen protectors - which add on to this because they scratch much easier than a phone screen would, making people think "wow, it's a good thing I used a screen protector!" even if it wouldn't have been a problem for them.

Because of the above, I don't think there is anything (reasonable) smartphone manufacturers could do to make people feel like they shouldn't add one just in "case".