Unless I'm mistaken, I have not seen this to be the case, I could be wrong and if so please provide links if possible. User session/login information retains within the application sandbox. So if a user could somehow share an application with another profile, then that data too would need to be segmented. Then all of a sudden people are back at user account administration. When you add or remove an account, then there is the management of session and credentials to manage per app. If you wipe the application, does it pull it from others? If so, what if you want the less to have the app, but you don't want it? In the mind's eye, "sure, how hard can it be, right?" In practice, this is why general purpose OS stink so badly.
Data shows (now I'm talking US families here) the average size of a family is 3, which is down from 4 in the 1960s. (
see US Census). The average family owns 2 smart phones and 2 computers, but typically has 10 connected devices; though some reach show upwards of
16. (see
PEW Research and
Statisa). Of the 10-16 devices, tablets float in the space as not a computer and not a smartphone and can be lumped with TVs and thermostats. (I hopes those stats change to reflect tablets as a personal compute module.) Though it's not hard data as no OEM is supplying this data, one can see most homes have nearly a 1 to 1 ratio of person to computational unit. The trending trajectory will be 2 personal devices per person in the US market in the next 3-5 years. Once again, emphasis on broad spectrum and not catering to demographics or economics.
With this in mind, multi-user accounts was really a means to reduce costs by purchasers, not as a means real functionality unless you are talking about servers. Also, multi-user accounts on platforms is also a ripe attack vector that has been exploited for decades. Look at any OS's security frameworks and it's an unruly mess for such a simple idea of "sharing the soup spoon around the bowl."
Sure, having multiple accounts will help the parents for the grubby hands pawing for the latest Paw Patrol or elementary needing their Doom-slaying fix/hit on another world in Minecraft. But the data just doesn't back the capital investment for such devices warrants the need for multi-account support. Now on shared experiences, like TVs, automobiles, etc. etc.., that makes a lot of sense. But tablets is really a one person device experience during use.
I think iOS 18 will take a bit of pressure off as you can lock down individual apps from those Cheetos powered fingers. It should accomplish the same outcome.