You consented to their being able to delete it when you agreed to their terms of service. It’s like if you hire someone to clean your home. Mostly they’re tidying up and dealing with dirt and dust, but if they see what looks like a used napkin lying somewhere, they will probably throw it out without first asking if you still want it - without that being stealing and without ever owning it themselves.

It may seem weird weird to compare useful content to a used napkin, but hey, successful business founder stereotypes do quite often involve have an idea written on a napkin…