The non-oral version of the explanation author received is likely 農地解放, a postwar US/Allied military led land reform.

The core idea of it, I think, is that those landlords must have been the mainsails of prewar Japanese military dictatorship regime and its expansionism under the strong leadership of its emperor, and breaking up land ownership will make it complicated for Japan to re-consolidate power and/or to somehow become closer to the Soviets.

I guess it did serve its core purpose of keeping China/Russia at bay, considering Japan has been extraordinary antagonistic to neighboring, and/or openly communist and/or totalitarian regimes, despite running on a rather ethnocentric communism-from-first-principle political system...

1: https://ja.wikipedia.org/wiki/%E8%BE%B2%E5%9C%B0%E6%94%B9%E9...