For the same reason AI can't draw an analog clock showing an arbitrary time like 5:19. The training data for wine glasses doesn't include examples of full wine glasses because wine is rarely photographed filled beyond a standard serving of wine. Same goes for clocks where only aesthetic clock hand positions are photographed rather than arbitrary times. AI is only able to mimic rather than be truly creative. This is just one more reason AI is nothing more than a parlor trick. It doesn't think, it isn't aware and it will never out-do a human mind for versatility. AI is just magic to lay-people but real thinkers know better.