Quite simply, clicking on anything within an EditorGUI.Foldout will result in closing the Foldout. Also, if the clickable label is disabled, you can’t interact with anything in at all.
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— expat1999
Found an answer to my own question in another Unity Answers post. It was probably worded better, judging by the comments on my own post, but here it is for those who may need it:
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EditorGUI.Foldout consumes click so GUI.Button doesnt work when inside of foldout region.
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The top reply makes use of EditorGui.BeginProperty, EditorGui.EndProperty as well as EditorGUIUtility.singleLineHeight (basically).