and phones are extremely hard to made truly air-gap
One very good argument is that a burglar will most probably steal that smartphone even if it's older, put a SIM in it and turn everything on, making indeed phones somehow risky for cold storage.
Another very good argument is that somebody in the house would do exactly that too (put a SIM in) because of not knowing it's a "special use" phone.
If someone should decide to use an Android phone wether old or new make for cold storage then it's expected that the person should have a secure hidden place place that by chance still wouldn't come to the thought of a burglar that anything of value like a phone could be placed there not to talk of a phone used as cold storage.
Like every home has some spot's where no one would ever believe that something of value could be kept there not even a member of the house either.