There are two reasons to install an app: I personally want to install it or a powerful third party will bring down a wildly disproportionate punishment if I don’t. Nowadays the vast majority of app installs are in the second category, and in this category, being able to make it common knowledge that I physically can’t install your (parking app / apartment app / course selection app /banking app) as root with unlimited privileges even if you (tow my car / evict me / expell me / close my bank account) is super valuable. This value skyrockets further if a large section of the population has this same inability to root themselves, which apple coordinates. This is why people buy apple! ask anyone who buys an iphone for grandma. I would be quite pissed off if the government steps in and takes away this coordination mechanism.
Your coordination mechanism is to just to rely on the good will of a single company. How long do you expect it to last before apple starts cooperating with invasive parking apps, banking apps, etc?
It is a little rough. On reflection, the scenario when apple would sell you a locked down phone and google would sell you a side-loadable phone was ideal- the locked down phone was in my opinion better for phone tasks, but apple couldn’t abuse that too much or I’d just switch to android. A scenario where everyone is selling locked phones could remove that necessary check.
