It makes perfect sense for Apple to optimize their devices for stability and max run time. These are arguably the most important features of any device.

Any other behavior, including offering the user power options (because many users won't understand them) would introduce a poorer user experience (abrupt hard shutdowns, constant need to charge) and likely sway some portion of non-tech users to purchase a different brand when they refresh.

At the end of the day the battery is replaceable and if you chose to buy an iPhone you're already aware that they it is a "premium" device.