As someone who implements these types of requirements, this suggestion just adds complexity where none is needed. In the software, and the database, and the backup strategy, and for the average user. Complexity requires time, money, and introduces bugs and user error.
Right now we are required by law to remove user data upon request (Europe). That law is strong enough to cover those who need it.
Are you suggesting that not inconveniencing developers is more important than a right to privacy? I'd have to disagree with you if this is the case.
I've worked both for companies that fall under extra scrutiny by government due to market position and for companies that deal with data that has strict retention limits. Yes, it increases complexity, but the laws that seek to protect people's privacy are far more important than any inconvenience to companies.
(And yes: in both cases there were regular audits and any lack of compliance had very real consequences)
Actually GDPR requires you to delete data when no longer needed. How long data is needed depends on what type of data it is. For example financial transactions are covered by other laws to be kept for certain amount of time. If data is linked to a survey that is completed then, by law, that data is no longer needed and should be deleted. How long should photo likes and comments be kept? I don't think there are good guidelines or judgements regarding this but it is nevertheless something to take into consideration and in most cases delete data based on age.
Right now we are required by law to remove user data upon request (Europe). That law is strong enough to cover those who need it.