What is the fundamental difference between art and science? Why?

Art comes from creative minds for all kids and adults but science is how to create money just by surprises like the covid vaccines and some hokus focus variants.

Real Science has the Scientific Method that gives it limits and parameters, a method. Art is really without limit or any certain method as far as the general term goes. Creativity itself is a product of the imagination, which if open, also really has no limits but those that the imaginer gives them.

The difference is in the absence or presence of justification. Science requires robust justification, art doesn't. Science is based on objective criteria, art only requires finance.

There are two paramount differences between art and science. The first is that art is subjective while science is objective. The second is that art expresses knowledge, most often in the form of subjective representation, while science is the system of acquiring knowledge.

The difference between reproducibility including the subjectivity of the observer.

In business, observers can lie. Some of their sensibilities sympathize with money.

Science is an attempt to determine the actual nature of that which exists outside of the mind. Art is an attempt to express that which exists within the mind. One, in a manner of speaking, brings the physical world into a conceptual world; the other brings a concept into physical being. Science is often used to create art. I think of engineers as artists that use concepts that scientists have created to sculpt their art. 

"Fundamental" becomes Oneness as the finite self realizes both Soul and Spirit, Mind and Life.

Also, Heidegger's apt concern in "What Is Called Thinking?" re techne and the spirit of a man is outpictured in the youthful nightmarish samizdat of a generation raised up in the surveillance matrix:  https://www.youtube.com/watch?v=PqrrnIFB7Gc 

Science is about "form & function"....Art is about "reception & impression".

As for the "why?" humans exist in both the practical and aesthetic world. In addition to our basic needs for food, shelter and clothing, we also have emotional (once could even say spiritual) needs for beauty and fulfillment.

There isn't a great deal of difference between art and science.  The difference comes how they're applied  in society.  Art tends to focus on creation, and science is more about testing

The fundamental reason - human psychology. When a composition is "right" it's just because that's the way the human brain likes it. We can argue all night and day about whether or not art and science are the same thing. I know a painter who says everything he does is carefully calculated. Well, some people are more intuitive than that.

A Victorian essayist and art critic named Ruskin wrote a book with rules of composition. They work IF you want to paint like a Victorian, not that there's anything wrong with that.