Your brain learns by mixing things up. Your knowledge is based more on comparison and contrast then hard factual data like a computer. So to really learn you need to come at things from different angles.
Your brain stores knowledge in what some call a mental model. These models are just approximations of reality. The more information the brain gets about reality the better they get. Mental models are molded by experience and analysis.
These models are complex and interconnected. So, giving your brain access to a breadth of experience will help you build better models across the board.
Mental models are often wrong and improving them is a major part of learning. I like to think of these models as lenses through which we see the world. You never directly see the world; you only see it through lenses which are inherently imperfect. Those lenses can be improved through testing and iteration.
Mixing things up lets you test your mental models under different conditions. Varying the ways you go about creating art (or anything really) lets you test your knowledge and skill.
When you fail to meet your expectations or just get an outcome you aren't happy with your brain learns there is a problem. It'll go about trying to fix that problem.
Mixing things up makes new problems more likely to emerge. Sometimes they're glaring and will directly inform your future study. For example you might realize you need to study perspective or composition.
Sometimes it doesn't feel like you're learning but every failed attempt teaches you something even if you're not conscious of it. And, for complex skills like painting and drawing, every attempt fails in some way.