The problem has multiple facets. Geometry is only one.

1. Cleanable geometry. Already discussed.
2. Additives in the plastic. Many plastics won't have been made around food safe equipment or may even have bad additives. Most 3D printing plastic isn't pure because most pure plastics don't print 'that' well (well, not as easily). They aren't expecting anyone to eat the plastic, so most make zero effort to keep unsafe (to eat) additives.
3. Temperature. Many of the easily printable plastics soften to the point of wilting below 100C. Sure, it won't crop up often, but put a large thin thing like a bowl in there, and I'd be surprised if it came out of a drying cycle unwarped.
4. Plastic around food. Most printed plastic is much softer than plastic utensils (not necessarily the "disposable" sort) at the store. There WILL be microplastics in your food with printed goods. (hell, depending on the task, plastic isn't a good idea even in many of the products at the store!) Plastic may be non-toxic, but so is asbestos. Asbestos is not chemically dangerous, yet it was outright banned, and doctors do not have a good idea what the presence of microplastics does.