Adams lost his bid for a second term. Jefferson, Madison and Monroe each served two terms. JQ Adams lost his bid for a second term. Jackson served two terms. Van Buren lost his bid. Harrison died in office, and Tyler was so unpopular and incompetent that his own party ditched him.
Polk was the one who decided not to run for a second term. When he ran the first time, he said that his sole goal was to annex the Republic of Texas into the Union, and if he succeeded, then he would not run for re-election. He was a man of his word.
Well, you’re amazing! Give yourself a star :-)