It's Apple. You are of course welcome to pay their exorbitant development fees yourself, go through the insane review process and publish your own competing app!
You can't publish your own competing app. The desired behaviour requires running a background service (not allowed) that watches arbitrary folders (not allowed).
Third party iOS apps do in fact have access to background tasks. There’s even a variant dedicated to longer-running tasks, like lengthy file syncs.
The difference is that instead of having an ever-running daemon, the developer schedules tasks with the system, and system decides when to run them based on network availability, battery charge, etc as well as the app’s behavior (badly written/inefficient background tasks and frequent high intensity task requests are penalized).
It may be the case that file eventing now works, but a quick check with an iOS dev friend suggests that the filesystem sandboxing is too restrictive to be meaningful anyway.
Further on this issue, consider that a functioning syncthing client is a node in a p2p network, so must be able to advertise and listen to requests in the background as well as the background jobs that NextCloud requires (as NextCloud is centralised it doesn't need node level co-ordination) - so a partially working NextCloud client is good enough, but a partially working Syncthing client is woefully broken.
Full agreement the above sounds silly. So really it comes down to line between the responsibility of the consumer, and the duty of the product creator to say what the product can or can not do.
If you really care about replacing parts in your car like the satnav, should you need to do research before buying instead of assuming it works that way?
Or should we have rules that all sat navs need to be replaceable so consumers don't need to do that?
I honestly can't draw the line myself, I just try my best to identify what I want in a product before purchasing. Especially huge purchases like a car.
For engaging in anti-competitive behavior. Forcing a single App Store on an os is much less draconian than offering a broken interface to basic OS functionality in order to prop your own product above others. Imagine if Windows downclocked whenever you wanted to use an office alternative. This is not much different.
correction: 30% of your revenue for certain business models. Still too much, but let's at least be somewhat accurate. Plenty of apps make tons of money on the App Store without every paying a dime to Apple beyond the $99.
