While not illegal, people should know when accounts change hands and it shouldn't go undetected.
They don't go undetected to people who know what to look for. Such things might include:
- change in posting style
- change in posting subjects & areas of posts
- change in knowledge of Bitcoin / blockchain / cryptocurrency / etc.
- change in local board language (that's a big one, lol)
- change in time zone or general times of posts
Besides, people sometimes receive undue flak for changing their password or email address, and recording these changes in a resource like BPIP would just contribute to this problem of arousing unnecessary suspicion.