Without sufficient technical information on how the computer works and without root access, we can't be certain a "wipe" will actually wipe everything.

For malware that could be inserted in a targeted manner, even with desktop computers we don't have access the every firmware of every part.

When we're talking about mobile "phones", we usually have an interface that tells us "sure, it's wiped", but is it? Without full root to every part of it, can you be certain that it is? When you press "wipe" on an iPhone or a closed Android flagship (or whatever the UI is), what happens exactly on the filesystem that you can't even access fully?

Telling people to hand over their devices willy-nilly is far from "good". We shouldn't settle for this. The hardware companies can ship us the tools to replace the battery ourselves. Maybe not "ourselves" - my aunt can ask me to do it for her if she can't do it on her own. But she trusts me more than she does people she's never seen ever. If the tools are expensive, we can ship them back. There are many options so we should discuss them.