Why did Republican Stalwarts support Taft over Theodore Roosevelt in 1912?

The Republican Party were initially attracted to Roosevelt's charismatic energy and appealing attitude. Roosevelt was passionate about many progressive issues, such as conservation and social justice, however, and became so progressive to the point that he began to displease the more conservative, GOP members. In addition, Taft was the incumbent president and party leader, giving him leverage over Roosevelt, and ultimately earning him the Republican nomination. As a result of this rejection, Roosevelt formed his own political party - the Progressive (Bull-Moose) party.