Because while the US Public and the Government could, did, and still do at times and to certain lengths tolerate discord between Generals and Civilian Leadership, one thing they have never shown a tolerance for is a military junta.

There is no time in the history of the US that a military dictatorship would have been sustainable, particularly not led by MacArthur who had as many bitter enemies in and out of service as supporters.

MacArthur for all his faults was still a General Officer in the Western and American tradition, that still meant respecting the authority of the process and the stability of government, when the Senate taking up his cause was not enough to restore him to power the game was up.

Any even hints at insurrection would have destroyed all his public sympathy. We also hen have the timing. 1952 was an election year. And the GOP's nominee was then the one military officer more well known than MacArthur in General Eisenhower, Ike had also a long history as a conciliator and consensus builder rather than the firebrand and agitator that MacArthur was.

And finally the biggest question would be where are the troops going to come from? As many soldiers hated as liked serving under him, and many famous and beloved Generals supported his sacking, including Omar Bradley who was the Chairman of the Joint Chiefs.