Per-account bans would also be easily exploited by those who do want to cheat - buy a game once, make five smurf accounts, add them all to a family, and get six fresh starts for the price of one. Any loophole like that absolutely would be abused.
This would give breath room for parents to explain to their kids that they should not cheat without leaving that much leeway for cheaters themselves.
Additionally, this only benefits people who share their game with cheaters - just don't do that. If you can't trust someone won't cheat with your copy of the game, they probably aren't a close family member.