Why do you suppose Roosevelt was elected four times...I have read all the books and looked at the legislation enacted by both Roosevelt and Hoover...Hoover believed in helping corporations, banks etc...he believed the markets would correct, but they didn’t.
1932. Bad economy, people blamed the incumbent, Hoover.
1936 FDR had bought off enough groups that even though the Depression within the Depression had started he had the groups and the GOP was in general disarray from its prior shellacking.
1940 Nation gears up for the war, starts supplying the Allies, war is on the horizon (Wilikie had a shot had it been an earlier election)
1944 mid-war, dicey time to change trains
1948 Truman, close call win - good strategy and negative campaign on his part.
Of course one could argue that the GOP was still somewhat in disarray in 1940 that they went with so recent a former Democrat as Wilkie.
Or I could offer a simpler explanation: At a time when America wanted a dictator, it got the closest to one that we have produced to date.