Part of these are social network effects (all my friends use it, plus the apps they use need you to use the same apps, meaning you have to use the same OS or one of the big ones, etc).
Part of them are actual network effects (you've already used the same g-suite or whatever apple provides, and moving to something else - if it exists at all - is either very difficult or impossible).
I'm sure there's others I am not thinking of right now.
But both leave only the "hardcore" privacy and open source activists as your only market - and that's so small that only others of similar persuasion even both to create and host those alternatives, if they exist at all. Since the market is small, and developers/time is lacking, UI and other parts of such apps/operating systems/ecospaces tend to be non-existant or suffer other oddities that keep them out of being adopted by the masses, unless those people get fed up enough with the existing products to be willing to put up with all the downsides of a more free and open system.
Which is kinda where Linux is today - a combination of becoming "good enough" - but also coupled with more than a bit of "corporate America" (and/or "corporate west") helping to make it just a tad better (for business use, for gaming, etc) - and the masses who are getting fed up with Apple and/or Microsoft - a few of them peel off to see what it's all about. Dual boot, or virtualization (and Microsoft has made that easier, too), they get a taste, and some think "hey this isn't really that bad - I can do almost everything" and some migrate over (with the big exception - games - but Valve and Steam are helping in that regard, too).
That's what is needed in the mobile realm, and nothing exists yet. Yes, there are alternatives, but the real bugger has been the hardware - which is very locked down, and only (again) the hardcore and activists are willing to go the extra mile to break open (root, jailbreak) consumer-available hardware, or purchase already "open" hardware, or go so far as to build their own hardware (I am contemplating this option, personally).
Until it gets easier for the "masses" to get a more open hardware mobile platform, the next step of an open ecosystem, operating systems, and apps is much for difficult to make happen. With Apple and Samsung being the main two hardware providers (for iOS and Android respectively), with the way both lock down their hardware, it will stay this way.
But really - for Android at least - Samsung does this mainly for the providers themselves. For instance (in my case), I have a G7 - but it's a T-Mobile version. I paid for it in full (I don't have a contract with T-Mobile, but they are my provider) - but Samsung provides a different version of the G7 (with a different processor and such) than they do outside the USA. That hardware is much easier to root, while the USA version is seemingly made to be as airtight as possible to root (with a constant back-and-forth game being played behind the scenes). It is strange - it's partly Samsung, partly the providers.
Ultimately, I'm just going to opt-out of this hardware game and build my own platform; I already have the 4G module to support phone and data (and I am planning on using it for data only, as I virtually never use my phone for voice calls). If I am lucky, it will be my winter project.
So true, which is why we need antitrust enforcement. If you run a platform or a service, you have to provide access to that platform or service to your competitors under the exact same terms as your customers. Anything less is the definition of anti-competitive.
In addition there is nothing stopping them for trading their iPhone for a more expensive Android.
I wouldn't be surprised if this is a likely outcome.
Documentation on iPhone hardware is basically nonexistent. Someone would need to reverse engineer it all and write drivers from scratch.