There are other reasons.
A big factor in the success of the iPad and maybe just some degree the iPhone, but especially the iPad, is that it’s “unbreakable”. All out restrictions mean it’s computer people don’t worry will suddenly stop working because they clicked to the wrong link. It won’t get a weird virus from their email.
That is a serious upside for a lot of consumers.
You can still have that. Make unbreakable the default, and add an "admin mode" toggle.
I feel like that same reason is why you see a lot of seriously tech-savvy people try to use iPads as laptop substitutes over and over even though they're obviously still not suitable for it for technical tasks. There's a lot of latent appeal in "okay, what if I just didn't have to worry about any of that ambient technical crap?".
They could allow unlocking the phone by burying that option deep in the settings with scary warnings etc. Most people could use the device with the restrictions. The fact that this is not possible at all is greed.