My understanding is that there was quite a large stock of Red Hackle put up before the war and it was all that was available during and immediately after. When the 50s came, people were ready to move on.
There was plenty of it on Ascension Island during WWII when my father was stationed there. The MSgt running what passed for the Officer’s Club collected empty bottles of other brands from aircrews passing through and filled them all with Red Hackle. In time subsequent crews would marvel over his wide selection and even argue over who’s brand was best—but they were all drinking the same thing.