It makes sense that it’s only phones that are jailbroken (and have not had the security passwords changed) because they can run any software..
If you are familiar with Apple computers at all, you will know that in order to get a virus on a Mac (yes I know that there are only 3 of them that exist), you have to authorise the virus to run on the computer. So if you got a virus on a mac, essentially it is your own fault because you told it to run..
Now, if the iphone is allowing any software to run, it is essentially allowing malicious software to run immediately because it can use the default password. So you don’t actually need to give it authorisation because it already has it.
If the user changes the password for some setting in the iphone (not sure what it is buts ure you can find it in one of the articles), even though its jailbroken, it will not be susceptible to this attack.
Hope that makes sense 