Or some overzealous engineer said hey guys let's delete all data 7 days after an account is canceled. This is called over optimizing.

Such a decision is just as likely to have come from the legal/compliance team as an engineer. Data you no longer have clear consent or a legitimate business need to store is a liability, and if you operate in Europe, potentially illegal to continue storing.

It’s amazing how much stupid shit we do to keep the legal guys happy while their bosses are busy engaging in <checks news headlines%> tax evasion, graft, bribery, fraud, embezzlement, illegal dumping, sexual harassment, sexual assault, statutory rape, solicitation to commit murder, and my personal favorite and I’m sure yours too: human trafficking.

But sure, we can break all of our users to avoid the possibility of you having to write some legal briefs and us paying a small fine for keeping data 7 days instead of three.