Tender is the Night was published January through April, 1934. As an exercise in understanding, I am going to list a few things that were happening in 1933 through 1935 in the United States (per wikipedia):
The U.S. was in the midst of a deep depression. 25% of the workforce was unemployed. FDR implemented the first New Deal beginning with his inauguration in March, 1933.
Bonnie and Clyde began the rampage that would ultimately end their lives by murdering two young highway patrolmen. They were shot dead on May 23, 1934, after their behavior transfixed the nation for two years.
The Dust Bowl began on November 11, 1933, in South Dakota. In May, 1934, a two day dust storm removed massive amounts of Great Plains topsoil in one of the worst such storms of the Dust Bowl. The dust clouds blew all the way to Chicago, where they deposited 12 million pounds of dust.
This is what it looked like in America:
This is what Fitzgerald was writing about:
In an epically self-indulgent book about rich, pretty people with rich, pretty people problems, like what to do when you drink too much booze, have sex with beautiful actresses half your age, and generally behave like a hollowed out husk of a human being.
Is it any wonder that it flopped?
In the final analysis, sure, it had redeeming literary value. But the characters were soulless and charmless (as Fitzgerald's characters often are) and the world that they lived in was shallow and superficial. It left me utterly empty. Sort of like Dick and Nicole Diver.