It’s always amusing when people who aren’t engineers assume something must be simple to make. Please show me a Nokia phone that was as thin as a current iPhone, with auto focusing video cameras (aka moving parts), and had a user-replaceable battery. I’ll wait. Samsung’s galaxy phones caught fire because they tried to make it just as thin with a user-replaceable battery (leading to short circuits), so that’s yet another thing you have to prevent in your hypothetical “it’s easy!” phone. Oh and it has to be rugged enough to withstand multiple drops like current phones AND not lose any of that thinness.

Edit: okay the galaxy battery wasn’t replaceable but you still need to make higher tolerances in a user-replaceable item to prevent that, meaning it cannot be too thin for safety reasons.