It makes sense though. When you are buying fanart you are buying a physical object. Something you can hold and own. It can be scanned and shared but you will own the actual copy.

Are you unaware of that fact that a significant number of commissionable fanartists work 100% digital? Any physical copy they give you of their .psd/.gif/.jpg/etc. ain't gonna be any different than if a fanfic writer printed their .doc/etc. and mailed you a pretty copy in a folder or something.