It is because they are tasked with the preservation of the United States as a political entity.

Anything or group that threatens the power of the state becomes their target - those targets evolve with time.

Socialism did not threaten the preservation of the United States as a political entity. Or the power of the state. It threatened specific interests.

From the perspective of the executive branch it very much did. Arguably still does, depending on your political persuasion.

Anti socialists claim socialism gives the state too much power. Not too little. Inarguably mixed economies are dominant and stable. Inarguably almost all countries with any history of self described socialist government persist. And American governments have an established history of acting on less than existential interests.