Narrow gauge in Wyoming?

Please forgive an ignorant foreigner, who has read too many Longmire novels
For one reason or another, despite having never visited, I have a fondness for the state of Wyoming. Good cattle country and the like. In Hiltons book, there is no mention of any narrow gauge in Wyoming. Montana, Idaho, Utah, South Dakota and Nebraska had narrow gauge roads, and I'm sure I've heard there were one or two in Colorado. It appears that North Dakota and Wyoming are the only western states with none. Can anyone suggest why this might be?
Wyoming doesn't appear uniquely different from its neighbours in geography, geology, agriculture. Was it just too well served by the union Pacific and the CB&Q that no-one was tempted to promote a narrow gauge?
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