Fragmented system, no single set of instructions will work everywhere and should be tailored for specific manufacturer, no updates after 2ish years, more suitable for tech illiterate as most teens are, and also parents prefer to use that for better parental control too. Android used to be the king of the hill pre-2014 era, after that, you get the worst of both words, the android downside and the iphone downsides (locked bootloader, etc.)