Can I upload software to my SIM card? No.
Most phones accept some type of SIM card, while not all phones have a means of user-controlled offline external storage (microSD, etc.).
Why can't the user access a SIM card? Why can't she look at the software stored on a SIM card?
The SIM card slot is pretty much off-limits to the user. Yet the user owns the phone.
This is like buying a computer that has a special card slot owned by a single company or a consortium of companies that produce special cards only for their own use. The user is effectively denied access to the slot.