They don't necessarily make better art but they do make rarer art. Because determining what is art, let alone what art is better then another, is truly a subjective thing it can be almost impossible to ever say any art is better then any other, however what everyone can agree on is how rare art is, this is a tangible thing. Once an artist dies the amount of their art that exists will never increase, only stay the same or even decrease and this makes their art inherently more rare.
Thus if you find a dead artist, whose art some people like, their art is going to be inherently more valuable and thus arguably more desirable then the art of some one still living and creating new art even if just as many people like that persons art as the art of the dead person.
The bunnies of Lavato have special abilities, like 'Action Skill: Make Carrot Disappear.'