In some countries there are laws such as GDPR, which oblige the service provider to keep customer data as long as it is necessary. It is true that they tell you that they delete it, but they do not. The best you will get is that it will not be sold or deleted after 5 years or 10 years according to the local law and the desire of the platform. In preserving the privacy of its customers, most platforms do not want to do that.
It's the first time I see someone invoking GDPR in order to use it against customers rights. AFAIK the General Data Protection Regulation (GDPR) has been made for protecting the privacy and the rights of individuals and to impose obligations onto organizations that collect, process, and/or store their datas, not the opposite. It focuses on ensuring transparency, consent, and secure handling of personal information, not on collecting and storing them how they want.
https://gdpr-info.eu