Developers are generally intelligent people but unfortunately many users are not. Sandboxing is for those people and it does its job well.
I do think however that there is a case for allowing a vendor-level sandbox so that apps made by the same vendor could share data amongst themselves.
This would facilitate free-trial to paid app upgrades.
In any case, give it time. Apple tends to start off with a solid base and build from there (rather than throwing everything onto the wall to see what sticks).
Developers are generally intelligent people but unfortunately many users are not. Sandboxing is for those people and it does its job well.
I do think however that there is a case for allowing a vendor-level sandbox so that apps made by the same vendor could share data amongst themselves.
This would facilitate free-trial to paid app upgrades.
In any case, give it time. Apple tends to start off with a solid base and build from there (rather than throwing everything onto the wall to see what sticks).