Replaceable batteries should be top priority.
All this engineering to make them smaller is a waste of money when everyone puts them in some kind of protector anyway.
But if you make the device larger -that doesn’t diminish the need for a protective case - which means an even BIGGER package after all is said and done.
Consumer demand - it is what the free market/capitalism is all about. The vast majority of consumers want bigger screens, but smaller and lighter devices overall. They don’t want a brick -