Most computers (which due to all we've done to them, phones ARE classified as one) , come with a ton of extra crap that realistically, we'll never/rarely use. In the case of a hand me down or refurbished one, there's crap from the previous owner, or from the technician that restored it. And then, for the typical store-bought ones, the manufacturers/developers think we need/want all this extra junk, and in many cases, they integrate it with the operating system so extensively, or they put tight security restrictions on them, that it is extremely difficult, or even risky, to remove.
In the second scenario, the solutions all tend to involve carefully hacking/modifying the device/system in question. Seeing as they're not designed or intended to do that, there's a risk of screwing stuff up, and I'm pretty sure it can void the warranty. One of the biggest complaints about the Windows operating system starting at Vista, actually has been that the OWNER of the computer has very little control over what it does, because the system locks them out of virtually everything in the interest of "Security". I also have heard talk that Windows 10 has keyloggers built-in. As far as phones are concerned, I can't say a whole lot. I have had friends with iPhones and Androids. I don't have either, I do know there are ways to hack/modify them if you're not satisfied with their intended/default functionality.