They said they don't bother because it's non-trivial to implement convincingly, so they don't bother, lest it gives people a false sense of security. For instance, if you do this, and the adb logs aren't scrubbed, then that's massively suspicious and that'd still you in legal hot waters.
It would be easily detected by widely used forensic software from Cellebrite and other companies. It would also definitely look suspicious. We explained in much more depth in response to a related proposal:
Can you pay someone or have a volunteer manage the social media? Seems like not a good use of an insanely skilled developer's time to reply to people on twitter so much. Obviously you should write the explanatory posts.
People are doing that in Belarus (since 2020 the repression still continue). You also need to create a convincing profile and story for all the usual apps. Alibi if you wish.
Not forensically safe. I guess the authorities are aware but don't take the steps all the time except important cases. Really puts the citizens on their toes.
im not sure if grapheneos does or not, but it's not a novel idea, and often will only be a delay tactic.
forensics will reveal the other partition(s), and then you're in the exact same position having to answer "what's the other partition, provide the password"