President Franklin D. Roosevelt is the only American President to give more than two Inaugural Addresses. This is due of course to the fact he is the only president to serve more than two terms.
The Third FDR Inaugural Address was 1343 words long. By contrast, the Fourth FDR Inaugural is only 558 words. His second one was 1808 words by contrast. (Even at the wordiest, FDR can not compete with William Henry Harrison who had a 8442 word Inaugural Address!)
In 1941, FDR had been president for eight years and was facing likely war. In 1945, he had been president for twelve years and had endured being the leader of a country which was still being involved in one of the most brutal wars in history. Clearly, a sick and tired FDR was slowing down.
Of course, by the fourth time, maybe giving an Inaugural Address had lost all thrill and was just another chore to complete. Or maybe nothing can be read into these ceremonial speeches anyway.