> Almost everyone I know has a case on their phone
I don't think people put cases on their phone to make them thicker. I think they use cases to increase durability. Making the phone itself thinner means that the phone in a case will also be thinner, so that's perfectly compatible with the claim that people prefer thinner phones.
In my case - in the case of everyone I've chatted with that has a camera bump - it's to reduce the risk of damage to (or caused by) the camera bump. Otherwise, most of them would get a significantly thinner case, the rest getting no case at all.
1) Sharp corner in a material - creates a weak point.
2) when set on a flat surface, it creates an unstable bridge, meaning downward pressure on the phone is not supported. Think of how a piece of cardboard would react to being pressed down in the middle with only 3 of its corners supported.
3) It creates a point that can be snagged when moving the phone around, either on clothing or surfaces it's set on.
Personal opinion, it's really frustrating to have a phone that doesn't sit flat on a surface, to be unable to easily use it without some kind of case or holding it.
I don't think people put cases on their phone to make them thicker. I think they use cases to increase durability. Making the phone itself thinner means that the phone in a case will also be thinner, so that's perfectly compatible with the claim that people prefer thinner phones.