You will probably get a variety of opinions to your question and perhaps you might consider posting it to a discussion group. I will give you my opinion. Fantasy in literature and in art represents a means of escape into another world, another existence. The reason there has been so much fantasy in art and in literature in the 20th century is because that century saw two devastating world wars which included most of the major world powers. The wars redrew the map of Europe and destroyed the economies of many countries. Thousands were killed. The Holocaust, the Stalinist purges, the Korean War, the Viet Nam War.........you get the picture. These are things that people want to escape from, so many writers and artists found that fantasy was a way to do this. As an example, C. S. Lewis wrote his Chronicles of Narnia series during this time, a series of fantasy stories and allegories that attempted to underscore what Lewis believed were the greater truths of life, things that could give mankind hope during a time when there seemed to be no hope.
Also, the 20th century was a time of incredible developments in science and in space. Man went to the moon. So naturally, this inspired an entire genre of science fiction fantasy. Perhaps life on other planets would be better than life on earth?
It will be interesting to read others' opinions.