I think that as a private citizen we are entitled to wipe our private phones as often as we like.. Yes it could be to hide crimes.. but there's not really anything anyone can do about it if we did wipe our phones..
I can't comment on the other scenario you mentioned, it seems perhaps different if it's a work phone, unless the policy is to wipe them regularly
These were government phones and the gov is supposed to archive the information on them. The people also knew the there is an investigation into the beginning actions of the Russian collusion investigation.
Had I wiped my personal phone clean after knowing law enforcement wanted to examine it...I would be in jail.