Right. For most (American) companies (I don’t know about GDPR-folks), “delete” means “hide from requesting user” not “remove data from internal system.”

Data is (at least a big part of) their business and they don’t further that end by removing data.

Of course it’s shitty, but it’s industry standard practice. It’s similar to the Facebook shadow profile you have when you don’t even have a Facebook account: you can ask them to delete your direct data, but they’ll never remove the implications they learned from that data.