At the moment, we do not have the option to restrict people creating deals without associating a contact, however, as a solution I will suggest that the owner of the deal be a mandatory field when creating offers. This way it will be known who is the person creating those offers without the association.
If this option is something you'd like to try, here's a quick video with the steps.
On the other hand, another option could be to make contact association mandatory, I've been checking and found this idea, it's already in status> Being in review, you can vote for it and follow to receive updates 🙂