I see what you're saying but this has never been done before. BIOS passwords could be bypassed by draining the battery. Encryption is practically the only way to protect your data, because the storage can be taken out of the phone and hooked up to something else if need be.
Making a new OS is just the easiest way for Apple to do this; there are other ways.
While I agree, this is not what OP's comment was about. He makes it sound like Apple is forced to write a decryption tool that exploits existing backdoors into the encrypted content.
Highly ironically, the current "Error 53" hullabaloo is exactly about what happens once security it tightened to the extreme.
The iPhone in question is protected with an unknown passcode. Auto erase is enabled, so brute-forcing the passcode will erase the data.
However, a new OS version without auto erase and that accepts passcode input from USB would allow the FBI to try all combinations.
How is Apple at fault because most any passcode scheme can be cracked via brute-forcing all comginations?