My iPhone has THOUSANDS of features. Battery life, interoperability with other devices, reliability, familiarity, particular apps that I’ve purchased already, and hundreds of other reasons all contribute to why I like one smartphone brand over another.
And yes access to third party apps is one of those thousands of contributing factors but ultimately I’m not going to buy a phone that has a crappy battery and doesn’t work with any of my other devices just so I can download a couple extra cool apps without the App Store. Besides I can jailbreak this iPhone (at a privacy risk since I have to flash the whole firmware) and run sideloaded apps if I want to but it’s usually not necessary.
So you keep equating making a choice based on thousands of variables with a large scale consumer endorsement of one particular variable which is not at all scientific or logical.
For the average consumer, the fact that they have $200 in iOS apps they’ve already purchased over the last decade and their entire family is on Macs and iPhones that have generally been reliable is enough reason to stay with another iPhone. They’re not thinking about walled gardens when they’ve probably never even realized the distinction.