Ironically, they also have a feature to extend battery life by throttling the CPU when the battery is low, and this made people complain that Apple was trying to force them to buy new phones with a secret virus that made their phones slower by throttling the CPU for no reason.
Batteries are wear items, and they stop working as efficiently as they wear. That can mean reduced battery life, but also reduced battery stability where it has random voltage drops when the CPU activity spikes.
There are two methods to deal with this. You can go the Android way and if your CPU tries to draw more power than your battery can supply, your phone just reboots. The Apple way was to slow your CPU down so it CAN'T draw more power than the battery can supply, so your phone stays running and useable, but at a slower rate depending on how bad the battery is.
Did Apple choose to slow the CPU too much? Maybe. Should they have been more up front about the entire situation so it doesn't become a bigger conspiracy than it did? Absolutely. Nobody likes Apple's smug "we know what's best for you" but at the same time, that mindset is what allows them to polish their walled garden into a beautiful, golden prison.
What's worse than the iPhones is the Macbooks, where they don't let you run 32 bit programs on CPUs that absolutely can because they removed 32 bit compatibility in newer versions. They are even worse than Microsoft when it comes to making app developers use their newest OS methods for things so that something like Discord can no longer run on older versions once Discord drops the old methods.
Nothing like trying to open a program that worked yesterday, but doesn't anymore.
