so make a removable battery!! you can sugar-coat more colors on the phone but can't design a replaceable battery compartment??
A replaceable battery would make the battery smaller.
Survey after survey confirms that most people who own phones with replaceable batteries don't own a 2nd battery anyway.
Thus, putting a replaceable battery in an iPhone will make battery life worse for the majority of Apple's customers.
Something that makes the phone worse for most people = Something Apple is not going to do.