Why do people fail to appreciate the art in their era?!

Painting by Claude Monet
Why is that an artists’ work frequently recognised and appreciated so late in the art world? After all, the artwork doesn’t change with time, it stays the same, but the audience who admire their work grows with the passing eras; why?!
Though we are living in the 21st century, there are no significant changes in this practice. As a result, many of them lack to witness their work’s success during their existence.
All of them believed in their passion and the art they were creating; it was the only thing that constantly kept them going despite their repeated failure in the art world.
So, don’t they deserve to be appreciated in their time by their society?
Vincent van Gogh, a post-impressionist Dutch painter, is one of the renowned painters of all time. His painting, “Portrait of Dr Gachet,” was sold for $82.5 million ($161.4 million today), making it the world’s most expensive painting to be ever sold at that time. Still, during his period, he was seen as the crazy one, the misfit and as a colossal failure in the art world.
Many failed to understand the emotions, actions and feelings he tried to capture with his paints. As a result, he died poor and depressed due to a lack of success.
“Despite everything, I shall rise again: I will take up my pencil, which I have forsaken in my great discouragement, and I will go on with my drawing.”
– Vincent Van Gogh 
Claude Monet, an artist who started the impressionist period with its ‘Impression, Sunrise’ painting, wasn’t well appreciated or understood in his time. His art was excluded by society and the museum exhibits then, but today his paintings cost between $7 – 81 million.
Followed by a close friendship with Vincent van Gogh, Paul Gauguin, a post-impressionist painter, suffered the same fate as him. He never got the success and appreciation that he so wished and desired for in his time either.
People saw his work as flat and meaningless. It was not until the 1940s that his work saw widespread success and appreciated by a larger audience.
“Life being what it is, one dreams of revenge.”
– Paul Gauguin 
Johan Vermeer, El Greco, Paul Cezanne (considered as the father of modern art), and the list goes on, and it’s just heartbreaking to know that most of them didn’t even witness their success; they died with an assumption that they were a failure in this world. Isn’t it sad?! 
Most of them died poor and hungry, but now their paintings are sold for millions of dollars; isn’t it unfair to the artist? They give their time, effort, and soul to work, only to see it and themselves failing in society without any money, appreciation or recognition.
They would have given a great deal to be appreciated then and see themselves as a success than a failure.
All the artists are trying to capture the poetry of the world they live in, be it on paper, canvas or any medium that they get.
There is something extraordinary inside all of them, and with the art, they are trying to express their beauty.
So, doesn’t the artist deserve to witness their success in the art world than dying without realising their value?
Read about ‘The afterlife of an artwork’ here