Since the earliest days of iOS, Apple has kept tight control on its users’ relationship with apps. The very first iPhone, of course, only shipped with a dozen or so preinstalled software programs: you couldn’t add more, you couldn’t delete the ones you had.
Over the years, Apple has loosened those strictures a bit. First you could add new third-party apps. Later, developers were even able to create and sell software that competed with some of those default options. More recently, you’ve even been able to delte some of those built-in apps. (Adios, Stocks!)
But more than a few restrictions have remained nonetheless. Most obviously, the prohibition on installing software from anyplace other than the company’s own App Store. I don’t take particular issue with that; the prevalence of malware and security breaches these days means you can’t be too careful, and Apple’s approach has had proven merit.