Because iOS devices are single-user by design. Think of the amount of cruft you could cut from your average desktop OS if you didn't have to support multiple users.
(I assume that, being UNIX under the hood, there actually are multiple users on an iOS device, for security. But these would presumably be invisible to the user, and not usable as login accounts).
Have a button somewhere that lets you switch to a different user. When you switch, you enter that other user's PIN or password. Then you see their apps, have their data, etc. When you switch back, you see your apps, have your data, etc.
It doesn't have to be very complicated. Even on a Mac, the "cruft" amounts to my name sitting in the menu bar, and having to choose who to log in as before I put in my password.
It sounds simple but it's not. Take android for example, i thought i could quickly set up a guest/party account without my email and things like that. Creating the account and selecting the allowed apps was very easy, the problems came later.
First, all my system settings wasn't cloned, to the new account i had to re-add things you take for granted like my localized keyboards and stuff like that, can't remember if wifi passwords were included or not. Then comes application settings, many apps are unusable before you configure them properly, even the web browser is unusable in the default state on high dpi devices, you must change the default zoom level. Then it seems some apps actually share state, and in some cases rightfully so, finding out how they share it is a mystery. Some are designed with multi user in mind so you can in fact have a mail app accessible on both accounts without sharing your mails as the system accounts are linked to different mail accounts. Others are the other way around, maybe you want your 10GB music collection to be accessible from every account? Drawing the line of where and what should be shared is very difficult.
I find it odd that your first comment is a complaint that setting up a new user actually acts like a new user. Of course your settings didn't carry over. That's the whole point of separate user accounts.
I see no need to overcomplicate it. A user account system where each account acts like a separate device (aside from the unfortunate realities of sharing storage resources) would be fine. What apps share state? None! What music gets shared? None! What settings get shared? None!
On fixed hardware devices things are a bit easier, but consider a desktop PC with Windows. If i install a driver for my new printer, should user B also have to install that driver? Should every family member have to install a printer driver?! To make things even worse replace printer with something necessary to even run the system properly like graphics card driver. Another food for thought is windows update.
I consider the keyboard localization in android to be of similar system-wide-configuration kind and shouldn't have to be redone for every user, someone else might not. (As a side note changing to a localized keyboard in android is in fact much harder than installing a driver in windows).
When does something cross the line from "system wide driver/configuration" to "user specific data/configuration"? If absolutely everything should act like a separate device you might as well dual boot or use virtual machines.
One of my scenarios for shared data is that when I'm working i want to listen to my music, but when i have a party i want to use the same device as a jukebox with the same music but not open up access to my documents. I know that i'm not alone with this problem. Trusting your friends to not dig around is another topic but with pop up notifications and active widgets on the desktop even your most trusted friends might get private emails shoved in their face even if they are trying to avoid them.
OK, but we're not actually talking about desktop PCs, but iOS devices. There are no drivers to install. There are almost no device-wide settings at all. Exceptions would be OS updates and stuff like Find My iPhone. Easy solution there: allow one and only one "owner" account to touch them.
The idea that keyboard localization should be system-wide is weird. Different people can speak and write different languages. Although it should be a non-issue, since a single person can speak and write multiple languages, and switching keyboards should be trivial.
Anyway, you can come up with scenarios where my "make it act like a fresh device" idea is inadequate. But my idea is still an absolute improvement over what we have now, and would be perfectly good for a lot of uses. You're describing a bunch of stuff you want but that is by no means required, and then using the complexity of that stuff to say that the whole feature is a bad idea. It doesn't make a lot of sense.
Yes. How is that circular? The OP is asking why he can't create separate logins on iOS devices. My answer: because Apple decided to make them single-user, presumably because of the simplicity and UX benefits to be had from that.
> Why can't I create multiple accounts? I want this feature.
> Because iOS is single-user.
It's not circular sorry, I meant to say your answer is stating the question.
I don't mean to offend or start a fight. I just read the conversation similar to "I have X why can't I have Y" "Because you have "X". The "by design" is moot when Apple are the designers. It's not some real world construct or difficult problem to solve, they don't have multi-user because they don't want IOS to have multiuser.
(I assume that, being UNIX under the hood, there actually are multiple users on an iOS device, for security. But these would presumably be invisible to the user, and not usable as login accounts).