I do not think this is a medical question, but here is one answer.
This has to do with osmotic forces. Remember the old experient with a semi-permeable membrane? Take a container and put in a divider that allows water to pass through, but not larger molecules. Then dump something in one side, like sugar, and the side with the sugar then has a concentrated solution of sugar while the other side is just water. Since the sugar cannot diffuse across the membrane, it is stuck on one side. The natural physics however, is that the osmotic concentration of the two sides will try to equalize. So water fromt he side with nothing in it, will move across the barrier to the concentrated side until the two sides approach equilibrium.
there are other forces at work, but that is the main principle.
Sugar on the strawberries, creates a concentrated sugar solution on the surface of the berries. The water content (along with other flavors) is drawn out of the strawberries creating a juice.
I hope this helps.
I found a link to the classic example you ask about.
Have a great day!