Can’t I just operate my business as a DBA instead of forming an entity?

Yes, of course you can.  As a sole proprietor or even a partnership you can operate your business without forming an entity.  If your last name is not in the name of your business, then you will need to apply for a fictitious business name (FBN) in the county where you operate your business.  However, you will not have the liability protection that a corporation, limited liability company, or limited partnership provides.  Thus if somebody wants to sue your company (for instance, for a slip and fall), they can come after your personal assets in addition to your company’s assets.