To be fair, at least Android and presumably iOS grant apps by default no access to your files in modern versions.
The only way to get, e. G., an attachment downloaded via Thunderbird to a PC or another app is the share dialogue. A user does not access to the isolated app storage by default on an unrooted Android phone. For better or worse the young user is actually making the right choice here for their platform.
(This is also why making a backup of an Android phone is a nightmare when you aren't using a first party option. ADB is sometimes able to bypass it)