Part of that is the company doesn't even know what they do internally - sometimes it purges instantly, other times it gets marked deleted in a database table that never gets purged until the fifteen billion row table takes down the service.
Company that wants to know, knows. The more these data are to the core of their reason for existence the better and more current this knowledge is. Don't give these aholes a pass they never ever deserved, they don't have any moral higher ground or moral 'credits' to burn. openAI is not different.
At a tech company of >1k engineers, this gets audited regularly by a dedicated data retention team.