A lot of people agreed with you when "It's a Wonderful life" previewed on Christmas 1946 to mixed reviews. It went into general release in Jan 1947 and did rather poorly at the box office.
Thangs got worst for the movie when On May 26, 1947, the
Federal Bureau of Investigation issued a memo stating, "With regard to the picture 'It's a Wonderful Life', stated in substance that the film represented rather obvious attempts to discredit bankers by casting Lionel Barrymore as a 'scrooge-type' so that he would be the most hated man in the picture. This, according to these sources, is a common trick used by Communists. [n addition, [redacted] stated that, in his opinion, this picture deliberately maligned the upper class, attempting to show the people who had money were mean and despicable characters." Following the FBI letter which was release publicly, there were calls to ban the movie by anti-communistic groups. By end of 1947, the movie had lost over half million dollars and Liberty Pictures had written it off as a loss with no plan to re-release it.
The year following, Liberty Pictures folded and many of the master were lost. The remaining films went to Paramount and were shelved. Wonder Life had a rebirth in the 50's but the poor qualify due to determination kept it off the networks. In the 60's, Paramount got the film repaired enough so the networks could show it but it failed to get much interest and Paramount dropped it. During the major studio crisis of the 50's and 60's, many major films were not re-copywritered as required by the law so the copywrite for Wonderful life was lost.
In 1974 the move went into public domain which made it free to the local TV stations and networks. So each Christmas season viewer saw Wonderful Life over and over. It became a classic Christmas movie, some arguing the audiences had finally discovered it. Others say it became a classic because it was played so often.
In 1990, the film was designated as "culturally, historically or aesthetically significant" and added to the
National Film Registry of the
Library of Congress. The America Film Institute rated the film number 11 out 100 best movies of all times. So today it is a classic and considered one the best Christmas movies ever made by many people.